Patent application title: NOZZLE ASSEMBLY FOR AN INKJET PRINTER HAVING A SHORT DRIVE TRANSISTOR CHANNEL

Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A nozzle assembly for an inkjet printhead is disclosed. The nozzle
assembly includes an inkjet nozzle having an actuator for ejecting an ink
droplet from the inkjet nozzle when a resistive element of the actuator
is heated by an electrical current. A drive transistor provides an energy
pulse to the resistive element of the actuator, and control logic
controls the drive transistor. The channel length of the drive transistor
is less than 1 μm.

Claims:

1. A nozzle assembly for an inkjet printhead, said nozzle assembly
comprising:an inkjet nozzle having an actuator for ejecting an ink
droplet from said inkjet nozzle when a resistive element of said actuator
is heated by an electrical current;a drive transistor for providing an
energy pulse to said resistive element of said actuator; andcontrol logic
for controlling said drive transistor,wherein a channel length of said
drive transistor is less than 1 μm.

2. The nozzle assembly as claimed in claim 1, wherein said drive
transistor, control logic and said inkjet nozzle covers an area of less
than 20,000 μm.sup.2.

3. The nozzle assembly as claimed in claim 1, wherein the diameter of said
ink droplet is less than 20 μm.

4. The nozzle assembly as claimed in claim 1, wherein an aperture of said
inkjet nozzle through which said ink droplet is ejected has a diameter of
less than 15 μm.

5. The nozzle assembly as claimed in claim 1, wherein the velocity of said
ink droplet is less than 8 m/s.

6. The nozzle assembly as claimed in claim 1, wherein the volume of said
droplet is less than 3 pl.

7. The nozzle assembly as claimed in claim 1, wherein the energy of said
energy pulse is less than 1 μJ.

8. The nozzle assembly as claimed in claim 1, wherein the voltage of said
energy pulse is less than 10 V.

9. The nozzle assembly as claimed in claim 1, wherein said actuator
develops a pressure of less than 100 kPa within said inkjet nozzle.

10. The nozzle assembly as claimed in claim 1, wherein said drive
transistor and control logic are formed on a silicon substrate, and said
inkjet nozzle is formed over at least one of said drive transistor and
control logic.

11. A printhead comprising a plurality of nozzle assemblies as defined in
claim 1, wherein nozzles are spaced from other nozzles ejecting ink of a
same color by less than 25 μm in a direction transverse to the
direction of movement of a print media upon which ink is ejected.

12. A printhead comprising a plurality of nozzle assemblies as defined in
claim 1, wherein nozzles are spaced from other nozzles ejecting ink of a
different color by less than 400 microns.

13. The printhead defined in claim 11 comprising at least 2000 nozzles
fabricated on a single monolithic wafer.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]The present application is a continuation of U.S. application Ser.
No. 11/696,126 filed on Apr. 3, 2007 which is a continuation of U.S.
application Ser. No. 11/144,844 filed Jun. 6, 2005, which is a
continuation of U.S. application Ser. No. 09/807,297 filed Aug. 13, 2001,
now issued as U.S. Pat. No. 6,902,255, which is a 371 of PCT/AU99/00894
filed Oct. 15, 1999.

FIELD OF THE INVENTION

[0002]In international patent application PCT/AU98/00550, the present
applicant has proposed an ink jet printing device which utilises
micro-electro mechanical (mems) processing techniques in the construction
of a print head driven by thermal bend actuator devices for the ejection
of fluid such as ink from an array of nozzle chambers.

[0003]Devices of this type have a number of limitations and problems.

[0004]It is an object of the present invention to provide various aspects
of an inkjet printing device which overcomes or at least ameliorates one
of or more of the disadvantages of the prior art or which at least offers
a useful alternative thereto.

SUMMARY OF THE INVENTION

[0005]In accordance with a first aspect of the present invention, there is
provided an inkjet printhead having a series of nozzles for the ejection
of ink wherein each said nozzle has a rim formed by the conformal
deposition of a rim material layer over a sacrificial layer and a
subsequent planar etching of at least said rim material layer so as to
form said nozzle rim.

[0007]In accordance with a second aspect of the present invention, there
is provided an inkjet printhead comprising:

[0008]a plurality of nozzle chambers each having an ink ejection aperture
in one wall thereof and an actuator interconnection aperture in a second
wall thereof;

[0009]a moveable ink ejection paddle located within the nozzle chamber and
moveable under the control of an external thermal actuator through said
actuator interconnection aperture for the ejection of ink out of said ink
ejection aperture;

[0010]said external actuator being covered by a protective covering shell
around the operational portions of said actuator, spaced apart from said
actuator.

[0011]The protective covering shell can be formed simultaneously with the
formation of other portions of the inkjet printing arrangement in
particular with the nozzle chamber walls.

[0012]The protective covering shell can be formed by deposition and
etching of a sacrificial material layer followed by deposition and
etching of an inert material layer forming the covering shell.

[0013]The external actuator can comprise a thermal bend actuator.

[0014]In accordance with a third aspect of the present invention, thee is
provided a method of forming an inkjet printhead on a substrate said
method including:

[0015]providing a first substrate on which is formed electrical drive
circuitry made up of one or more interleaved layers of conductive,
semi-conductive and non-conductive materials for the control of said
inkjet printhead;

[0016]forming on said substrate at least one nozzle chamber having an ink
ejection aperture in one wall thereof;

[0017]providing a moveable ink ejection paddle within said nozzle chamber,
moveable under the control of an actuator for the ejection of ink out of
said ink ejection aperture;

[0018]and utilizing portions of at least one of said interleaved layers as
a sacrificial material layer in the formation of one or more of the group
comprising said actuator and said ink ejection paddle.

[0019]The sacrificial material layer can comprise portions of a conductive
layer of the electrical drive circuitry. The electrical drive circuitry
can comprise a Complementary Metal Oxide (CMOS) process and the
sacrificial material layer can comprise a CMOS metal layer.

[0020]The sacrificial material layer can be utilized in formulating the
actuator. The actuator can comprise a thermal actuator. The actuator can
be located external to the nozzle chamber and can be interconnected to
the ink ejection paddle through an actuation interconnection aperture
formed in a second wall of the nozzle chamber.

[0021]In accordance with a fourth aspect of the preset invention, there is
provided an inkjet printhead constructed by MEMS processing techniques
with a plurality of ink ejection nozzles each having a nozzle chamber, an
external thermal bend actuator having a proximal end anchored to a
substrate and a distal end connected to an ink ejection paddle within
said chamber;

[0022]wherein said external thermal bend actuator further comprises a
series of layers and includes a planar conductive heating circuit layer
which includes a first portion adjacent said proximal end forming a
planar conductive heating circuit for heating said thermal bend actuator,
and a second portion extending into said ink ejection paddle, said second
portion being electrically isolated from said first portion by means of a
discontinuity in said planar conductive heating circuit layer, said
discontinuity being located external to said nozzle chamber.

[0023]The planar conductive heating circuit layer can comprise
substantially titanium nitride. The conductive circuit preferably can
include at least one tapered portion adjacent the proximal end so as to
increase resistive heating adjacent the proximal end.

[0024]In accordance with a fifth speci of the present invention, there is
provided an inkjet printhead having a series of ink ejection nozzles for
the ejection of ink, each of said nozzles interconnecting a nozzle
chamber with an external atmosphere, each said nozzle having a first
meniscus rim around which an ink meniscus normally forms, and an extended
ink flow prevention rim spaced outwardly from said first meniscus rim and
substantially encircling said first meniscus rim, arranged to prevent the
flow of ink across the surface of said inkjet printhead.

[0025]The ink flow prevention rim can be substantially co-planar with the
first meniscus rim and can be formed from the same material as the first
meniscus rim.

[0027]The ink flow prevention rim and the first meniscus rim are
preferably formed from Titanium Nitride.

[0028]In accordance with a sixth aspect of the present invention, there is
provided a movable micromechanical device including a bend actuator
adapted to curve in a first bending direction and having a substantially
planar bottom surface, said bend actuator being formed on a plane
substrate on top of a number of deposited lower layers, wherein the bend
actuator is formed by a plurality of steps including:

[0029]forming a series of structures in said deposited lower layers, said
series of structures having a surface profile including a series of
elongate ribs running in a direction substantially transverse to said
first being direction.

[0030]The bend actuator can comprise a thermal bend actuator. The
deposited layers can include a conductive circuitry layer and can be
interconnected to the bend actuator for activation of the bend actuator.
The bend actuator can be attached to a paddle member and actuated for the
ejection of ink from an ink ejection nozzle of an inkjet printhead. The
deposited layer, located under the bend actuator can include a power
transistor for the control of operation of the bend actuator.

[0031]In accordance with a seventh aspect of the present invention, there
is provided a method of construction of an inkjet printhead having a
large array of inkjet nozzle arrangements said method comprising:

[0032]defining a single inkjet nozzle arrangement for the ejection of ink
from a single nozzle; and

[0033]utilizing a series of translations and rotations of said single
inkjet nozzle arrangement to form all the inkjet nozzles of said inkjet
print head;

[0034]said utilizing step including:

[0035]initially forming a plurality of nozzles in a pod;

[0036]forming a group of pods, each group corresponding to a different
colored ink dispensed from said printhead;

[0037]forming a plurality of said groups of pods into a firing group;

[0038]combining firing groups forming a segment of said printhead;

[0039]forming each segment together to form said printhead.

[0040]The inkjet nozzle arrangements can include a series of layers
deposited and etch utilizing a mask. The layers can include conductive
layers which are preferably etched utilizing the mask so as to form a
series of conductive interconnections. The conductive interconnects can
include interconnects with adjacent versions of the inkjet nozzle
arrangement which can comprise translated and/or rotated copies of the
inkjet nozzle arrangement.

[0041]In accordance with an eighth aspect of the present invention, there
is provided a method of operation of a fluid ejection printhead within a
predetermined thermal range so as to print an image, said printhead
including a series of thermal actuators operated to eject fluid from said
printhead, said method comprising the steps of: [0042](a) sensing the
printhead temperature of said printhead to determine if said printhead
temperature is below a predetermined threshold, [0043](b) if said
printhead temperature is below said predetermined threshold, performing a
preheating step of heating said printhead so that it is above said
predetermined threshold, [0044](c) controlling said preheating step such
that said thermal actuators are heated to an extent insufficient to cause
the ejection of fluid from said printhead; and [0045](d) utilizing said
printhead to print said image.

[0046]The step (a) can further preferably include the steps of: (aa)
initially sensing an ambient temperature surrounding the printhead; (ab)
setting the predetermined threshold to be the ambient temperature plus a
predetermined operational factor amount, the operational factor amount
being dependant on the ambient temperature.

[0047]The method can further comprise the step of: (d) monitoring the
printhead temperature whilst printing the image and where the temperature
falls below the predetermined threshold, reheating the printhead so that
it can be above the predetermined threshold.

[0049]The step (c) further can comprise applying a series of short
electrical pulses so the thermal actuators, each being insufficient to
cause the ejection of fluid from the printhead.

[0050]In accordance with an additional aspect of the eighth aspect of the
present invention, there is provided a fluid ejection device comprising:

[0051]an array of nozzles formed on a substrate and adapted to eject ink
on demand by means of a series of ink ejection thermal actuators actuated
by an actuator activation unit attached to said ink ejection actuators
for activation thereof;

[0052]at least one temperature sensor attached to said substrate for
sensing the temperature of said substrate; and

[0053]a temperature sensor unit;

[0054]wherein before a fluid ejection operation is begun said temperature
sensor unit utilizes said at least one temperature sensor to sense a
current temperature of said substrate, and if said temperature is below a
predetermined limit, to output a preheat activation signal to said
actuator activation unit, whereupon said actuator activation unit
activates said ink ejection thermal actuators to an extent sufficient to
heat said substrate, while being insufficient for the ejection of ink
from said array.

[0055]The at least one temperature sensor can comprise a series of spaced
apart temperature sensors formed on the print head.

[0056]The array of nozzles are preferably divided into a series of spaced
apart segments with at least one temperature sensor per segment.

[0057]In accordance with a ninth aspect of the present invention, there is
provided an ink supply arrangement for supplying ink to the printing
arrangement of a portable printer, said ink supply arrangement including:

[0058]an ink supply unit including at least one storage chamber for
holding ik for supply to said printing arrangement, said ink supply unit
including a series of spaced apart baffles configured so as to reduce the
acceleration of the ink within the unit as may be induced by movement of
the portable printer, whilst allowing for flows of ink to the printing
arrangement in response to active demand therefrom.

[0059]Preferably, the ink printing arrangement is in the form of a
printhead which is connected directly to an ink supply arrangement in the
form of an ink supply unit having an ink distribution manifold that
supplies ink via a plurality of outlets to corresponding ink supply
passages formed on the printhead.

[0060]In the preferred form, the printhead is an elongate pagewidth
printhead chip and the baffles in the ink supply are configured to reduce
acceleration of the ink in a direction along the longitudinal extent of
the printhead and corresponding ink supply unit. Preferably, the ink
supply unit has a series of storage chambers for holding separate color
inks.

[0061]Preferably, the ink storage chamber or chambers are constructed from
two or more interconnecting molded components.

[0062]In accordance with a tenth aspect of the present invention, there is
provided a power distribution arrangement for an elongate inkjet
printhead of a kind having a plurality of longitudinally spaced voltage
supply points, said power distribution arrangement including:

[0063]two or more elongate low resistance power supply busbars; and

[0064]interconnect means to connect a selected plurality of said voltage
supply points to said busbars.

[0065]Preferably the busbars are disposed to extend parallel to said
printhead and said interconnect means provide interconnections extending
generally transversely therebetween.

[0066]In a preferred form the interconnect means is in the form of a tape
automated bonded film (TAB film).

[0067]Desirably the TAB film electrically connects with said busbars by
means of correspondingly sized noble metal deposited strips formed on
said TAB film.

[0068]Preferably the interconnect means also includes a plurality of
control lines for connection to selected other of said voltage supply
points on said printhead.

[0069]The unit can be detachable from the power supply and the external
series of control lines. The conductive rails can comprise two
mechanically stiff conductive bars.

[0070]In accordance with an eleventh aspect of the invention there is
provided an ink supply unit for supplying a printhead containing an array
of ink ejection nozzles, said supply unit comprising:

[0071]a first member formed having dimensions refined to a first accuracy
and having a first cavity defined therein;

[0072]a second member in the form of an ink distribution manifold having a
second cavity defined therein, said second cavity being adapted for the
inserted of a printhead;

[0073]said second member being configured to engage said first cavity in
said first member so as to define one or more chambers for the supply of
ink to ink supply passages formed in said printhead;

[0074]said second member being formed having dimensions refined to a
second accuracy which is higher than said first accuracy.

[0075]Preferably, the first and second members are configured to together
define a series of ink storage chambers, desirably suitable for storing
different colored inks.

[0076]In the preferred form the second member defines a series of discrete
ink outlets that are adapted to provide ink to ink supply passages in the
printhead that are adapted to supply ink to grouped sets of ink ejection
nozzles.

[0077]Preferably, the second member has overall external dimensions that
are substantially smaller than those of the first member.

[0078]In accordance with an additional aspect of the eleventh aspect of
the present invention, there is provided an ink supply unit for supplying
a multiple color pagewidth ink supply printhead, comprising: a first
elongated member containing a series of chambers for the storage of
separate color inks and formed having dimensions refined to a first
accuracy and having a first elongated cavity defined therein; a second
elongated member including a series of wall elements and a second
elongated cavity defined therein, the second elongated cavity being
adapted for the insertion of a page width ink jet printhead, the wall
elements mating with corresponding elements of the first elongated member
to complete the formation of the series of chambers for the supply of ink
to a series of slots formed in the back of the printhead when inserted in
the second elongated cavity, wherein the second elongate member is formed
having dimensions refined to a second accuracy which is higher then the
first accuracy.

[0079]A screen for filtering portions of the ink supply flowing through to
the printhead is preferably provided, optionally as part of the second
member.

[0080]The first elongated member and/or the second elongated member can
include a series of baffles for reducing the acceleration of the ink
within the ink supply unit.

[0081]In accordance with a twelfth aspect of the present invention, there
is provided a method of interconnecting a printhead containing an array
of ink ejection nozzles to an ink distribution manifold, said method
comprising:

[0082]attaching said printhead to said ink distribution manifold utilizing
a resilient adhesive adapted to be elastically deformed with any
deflections of the ink distribution manifold.

[0083]In accordance with an additional aspect of the twelfth aspect of the
invention there is provided a printhead and ink distribution manifold
assembly wherein said printhead is attached to said ink distribution
manifold by means of a resilient adhesive adapted to be elastically
deformed with any deflections of the ink distribution manifold.

[0084]In the preferred form the printhead is an elongate pagewidth
printhead chip and the ink distribution manifold forms part of an ink
supply unit. Desirably the ink supply unit comprises:

[0085]a first elongated member containing a series of chambers for the
storage of separate color inks and having a first elongated cavity
defined therein;

[0086]a second elongated member including a series of wall elements and a
second elongated cavity defined therein, said second elongated cavity
being adapted for the insertion of a page width ink jet printhead, said
wall elements mating with corresponding elements of said first elongated
member to complete the formation of said series of chambers for the
supply of ink to a series of slots formed in the back of said printhead
when inserted in said second elongated cavity,

[0087]wherein said second elongated member is interconnected to said first
elongated member utilizing to a resilient adhesive adapted to be
elastically deformed with any bending of said ink supply unit.

[0088]The printhead chip can be attached to the ink supply unit along the
sides and along a back surface thereof.

[0089]In accordance with a thirteenth aspect of the present invention,
there is provided an inkjet printhead comprising:

[0090]a plurality of nozzle chambers, each having a nozzle aperture
defined in one wall thereof for the ejection of ink out of said aperture;

[0091]an ink supply channel interconnected with said nozzle chamber;

[0092]a paddle moveable within the nozzle chamber by an actuator and
operable to eject ink from said nozzle chamber, said paddle having a
projecting part which, upon operation of said actuator is caused to move
towards said nozzle aperture.

[0093]Preferably, the projecting part, upon activation of the actuator,
moves through the plane of the aperture and can be located concentrically
with the nozzle aperture.

[0094]The liquid ejection aperture can be formed utilizing the deposition
and etching of a series of layers and the projecting part can comprise a
hollow cylindrical column.

[0095]The hollow cylindrical column preferably can include an end adjacent
the aperture which can be chemically mechanically planarized during the
formation of the aperture.

[0096]The actuator can comprise a thermal bend actuator conductively
heated so as to cause movement of the paddle.

[0097]The projecting part can be located substantially centrally on the
paddle.

[0098]In accordance with an additional aspect of the thirteenth aspect of
the present invention, there is provided in an inkjet printhead having at
least one chamber from which liquid is ejected from a nozzle aperture
interconnected with said chamber by means of movement of a liquid
ejection paddle, a method of improving the operational characteristics of
said printhead comprising the steps of:

[0099]locating a projecting part on said moveable paddle, said projecting
part undergoing movement towards said nozzle aperture upon activation of
said liquid ejection paddle to eject fluid.

[0100]The projection part preferably can include an end portion which
moves through the plane of an outer rim of the aperture upon activation
of the liquid ejection paddle.

[0101]In accordance with a fourteenth aspect of the present invention,
there is provided an inkjet printhead apparatus comprising:

[0102]a plurality of nozzle chambers each having a nozzle aperture defined
in one wall thereof for the ejection of ink out of said chamber and a
second aperture for the insertion of an actuator mechanism;

[0103]an ink supply channel interconnected with said nozzle chamber;

[0104]a paddle moveable by an actuator operable to eject ink from said
nozzle chamber, said actuator including:

[0105]a first portion located externally of said nozzle chamber and

[0106]a second portion located internally of said nozzle chamber,
supporting said paddle;

[0107]an interconnecting portion interconnecting said first portion and
said second portion through said second aperture, said interconnecting
portion further including a protruding shield formed adjacent said second
aperture and positioned so as to restrict the flow of fluid through said
second aperture.

[0108]The shield can comprise a hydrophobic surface. The interconnecting
portion typically moves in an upwardly defined direction towards the
liquid ejection aperture, and the shield can be formed on a top surface
of the portion. The actuator preferably can include a thermal expansion
actuator located in the first portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0109]Notwithstanding any other forms which may fall within the scope of
the present invention, preferred forms of the invention will now be
described, by way of example only, with reference to the accompanying
drawings in which:

[0110]FIG. 1. illustrates schematically a single ink jet nozzle in a
quiescent position;

[0111]FIG. 2 illustrates schematically a single ink jet nozzle in a firing
position;

[0112]FIG. 3 illustrates schematically a single ink jet nozzle in a
refilling position;

[0113]FIG. 4 illustrates a bi-layer cooling process;

[0114]FIG. 5 illustrates a single layer cooling process;

[0115]FIG. 6 is a top view of an aligned nozzle;

[0116]FIG. 7 is a sectional view of an aligned nozzle;

[0117]FIG. 8 is a top view of an aligned nozzle;

[0118]FIG. 9 is a sectional view of an aligned nozzle;

[0119]FIG. 10 is a sectional view of a process on constructing an ink jet
nozzle;

[0120]FIG. 11 is a sectional view of a process on constructing an ink jet
nozzle after Chemical Mechanical Planarization;

[0121]FIG. 12 illustrates the steps involved in the preferred embodiment
in preheating the ink;

[0214]FIG. 107 is a side perspective view, partly in section, of a single
nozzle arrangement of the preferred embodiments;

[0215]FIG. 108 illustrates a side perspective of a single nozzle including
the shroud arrangement; and

[0216]FIG. 109-111 illustrates the principles of chemical, mechanical
planarization utilized in the formation of the preferred embodiment.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0217]The preferred embodiment is a 1600 dpi modular monolithic print head
suitable for incorporation into a wide variety of page width printers and
in print-on-demand camera systems. The print head is fabricated by means
of Micro-Electro-Mechanical-Systems (MEMS) technology, which refers to
mechanical systems built on the micron scale, usually using technologies
developed for integrated circuit fabrication.

[0218]As more than 50,000 nozzles are required for a 1600 dpi A4
photographic quality page width printer, integration of the drive
electronics on the same chip as the print head is essential to achieve
low cost. Integration allows the number of external connections to the
print head to be reduced from around 50,000 to around 100. To provide the
drive electronics, the preferred embodiment integrates CMOS logic and
drive transistors on the same wafer as the MEMS nozzles. MEMS has several
major advantages over other manufacturing techniques:

[0219]mechanical devices can be built with dimensions and accuracy on the
micron scale; millions of mechanical devices can be made simultaneously,
on the same silicon wafer; and

[0220]the mechanical devices can incorporate electronics.

The term "IJ46 print head" is used herein to identify print heads made
according to the preferred embodiment of this invention.

Operating Principle

[0221]The preferred embodiment relies on the utilization of a thermally
actuated lever arm which is utilized for the ejection of ink. The nozzle
chamber from which ink ejection occurs includes a thin nozzle rim around
which a surface meniscus is formed. A nozzle rim is formed utilizing a
self aligning deposition mechanism. The preferred embodiments also
includes the advantageous feature of a flood prevention rim around the
ink ejection nozzle.

[0222]Turning initially to FIG. 1 to FIG. 3, there will be now initially
explained the operation of principles of the ink jet print head of the
preferred embodiment. In FIG. 1, there is illustrated a single nozzle
arrangement 1 which includes a nozzle chamber 2 which is supplied via an
ink supply channel 3 so as to form a meniscus 4 around a nozzle rim 5. A
thermal actuator mechanism 6 is provided and includes an end paddle 7
which can be a circular form. The paddle 7 is attached to an actuator arm
8 which pivots at a post 9. The actuator arm 8 includes two layers 10, 11
which are formed from a conductive material having a high degree of
stiffness, such as titanium nitride. The bottom layer 10 forms a
conductive circuit interconnected to post 9 and further includes a
thinned portion near the end post 9. Hence, upon passing a current
through the bottom layer 10, the bottom layer is heated in the area
adjacent the post 9. Without the heating, the two layers 10, 11 are in
thermal balance with one another. The heating of the bottom layer 10
causes the overall actuator mechanism 6 to bend generally upwards and
hence paddle 7 as indicated in FIG. 2 undergoes a rapid upward movement.
The rapid upward movement results in an increase in pressure around the
rim 5 which results in a general expansion of the meniscus 4 as ink flows
outside the chamber. The conduction to the bottom layer 10 is then turned
off and the actuator arm 6, as illustrated in FIG. 3 begins to return to
its quiescent position. The return results in a movement of the paddle 7
in a downward direction. This in turn results in a general sucking back
of the ink around the nozzle 5. The forward momentum of the ink outside
the nozzle in addition to the backward momentum of the ink within the
nozzle chamber results in a drop 14 being formed as a result of a necking
and breaking of the meniscus 4. Subsequently, due to surface tension
effects across the meniscus 4, ink is drawn into the nozzle chamber 2
from the ink supply channel 3.

[0223]The operation of the preferred embodiment has a number of
significant features. Firstly, there is the aforementioned balancing of
the layer 10, 11. The utilization of a second layer 11 allows for more
efficient thermal operation of the actuator device 6. Further, the two
layer operation ensures thermal stresses are not a problem upon cooling
during manufacture, thereby reducing the likelihood of peeling during
fabrication. This is illustrated in FIG. 4 and FIG. 5. In FIG. 4, there
is shown the process of cooling off a thermal actuator arm having two
balanced material layers 20, 21 surrounding a central material layer 22.
The cooling process affects each of the conductive layers 20, 21 equally
resulting in a stable configuration. In FIG. 5, a thermal actuator arm
having only one conductive layer 20 as shown. Upon cooling after
manufacture, the upper layer 20 is going to bend with respect to the
central layer 22. This is likely to cause problems due to the instability
of the final arrangement and variations and thickness of various layers
which will result in different degrees of bending.

[0224]Further, the arrangement described with reference to FIGS. 1 to 3
includes an ink jet spreading prevention rim 25 (FIG. 1) which is
constructed so as to provide for a pit 26 around the nozzle rim 5. Any
ink which should flow outside of the nozzle rim 5 is generally caught
within the pit 26 around the rim and thereby prevented from flowing
across the surface of the ink jet print head and influencing operation.
This arrangement can be clearly seen in FIG. 11.

[0225]Further, the nozzle rim 5 and ink spread prevention rim 25 are
formed via a unique chemical mechanical planarization technique. This
arrangement can be understood by reference to FIG. 6 to FIG. 9. Ideally,
an ink ejection nozzle rim is highly symmetrical in form as illustrated
at 30 in FIG. 6. The utilization of a thin highly regular rim is
desirable when it is time to eject ink. For example, in FIG. 7 there is
illustrated a drop being ejected from a rim during the necking and
breaking process. The necking and breaking process is a high sensitive
one, complex chaotic forces being involved. Should standard lithography
be utilized to form the nozzle rim, it is likely that the regularity or
symmetry of the rim can only be guaranteed to within a certain degree of
variation in accordance with the lithographic process utilized. This may
result in a variation of the rim as illustrated at 35 in FIG. 8. The rim
variation leads to a non-symmetrical rim 35 as illustrated in FIG. 8.
This variation is likely to cause problems when forming a droplet. The
problem is illustrated in FIG. 9 wherein the meniscus 36 creeps along the
surface 37 where the rim is bulging to a greater width. This results in
an ejected drop likely to have a higher variance in direction of
ejection.

[0226]In the preferred embodiment, to overcome this problem, a self
aligning chemical mechanical planarization (CMP) technique is utilized. A
simplified illustration of this technique will now be discussed with
reference to FIG. 10. In FIG. 10, there is illustrated a silicon
substrate 40 upon which is deposited a first sacrificial layer 41 and a
thin nozzle layer 42 shown in exaggerated form. The sacrificial layer is
first deposited and etched so as to form a "blank" for the nozzle layer
42 which is deposited over all surfaces conformally. In an alternative
manufacturing process, a further sacrificial material layer can be
deposited on top of the nozzle layer 42.

[0227]Next, the critical step is to chemically mechanically planarize the
nozzle layer and sacrificial layers down to a first level eg. 44. The
chemical mechanical planarization process acts to effectively "chop off"
the top layers down to level 44. Through the utilization of conformal
deposition, a regular rim is produced. The result, after chemical
mechanical planarization, is illustrated schematically in FIG. 11.

[0228]The description of the preferred embodiments will now proceed by
first describing an ink jet preheating step preferably utilized in the
IJ46 device.

Ink Preheating

[0229]In the preferred embodiment, an ink preheating step is utilized so
as to bring the temperature of the print head arrangement to be within a
predetermined bound. The steps utilized are illustrated at 101 in FIG.
12. Initially, the decision to initiate a printing run is made at 102.
Before any printing has begun, the current temperature of the print head
is sensed to determine whether it is above a predetermined threshold. If
the heated temperature is too low, a preheat cycle 104 is applied which
heats the print head by means of heating the thermal actuators to be
above a predetermined temperature of operation. Once the temperature has
achieved a predetermined temperature, the normal print cycle 105 has
begun.

[0230]The utilization of the preheating step 104 results in a general
reduction in possible variation in factors such as viscosity etc.
allowing for a narrower operating range of the device and, the
utilization of lower thermal energies in ink ejection.

[0231]The preheating step can take a number of different forms. Where the
ink ejection device is of a thermal bend actuator type, it would normally
receive a series of clock pulse as illustrated in FIG. 13 with the
ejection of ink requiring a clock pulses 110 of a predetermined thickness
so as to provide enough energy for ejection.

[0232]As illustrated in FIG. 14, when it is desired to provide for
preheating capabilities, these can be provided through the utilization of
a series of shorter pulses eg. 111 which whilst providing thermal energy
to the print head, fail to cause ejection of the ink from the ink
ejection nozzle.

[0233]FIG. 16 illustrates an example graph of the print head temperature
during a printing operation. Assuming the print head has been idle for a
substantial period of time, the print Head temperature, initially 115,
will be the ambient temperature. When it is desired to print, a
preheating step (104 of FIG. 12) is executed such that the temperature
rises as shown at 116 to an operational temperature T2 at 117, at which
point printing can begin and the temperature left to fluctuate in
accordance with usage requirements.

[0234]Alternately, as illustrated in FIG. 16, the print head temperature
can be continuously monitored such that should the temperature fall below
a threshold eg. 120, a series of preheating cycles are injected into the
printing process so as to increase the temperature to 121, above a
predetermined threshold.

[0235]Assuming the ink utilized has properties substantially similar to
that of water, the utilization of the preheating step can take advantage
of the substantial fluctuations in ink viscosity with temperature. Of
course, other operational factors may be significant and the
stabilisation to a narrower temperature range provides for advantageous
effects. As the viscosity changes with changing temperature, it would be
readily evident that the degree of preheating required above the ambient
temperature will be dependant upon the ambient temperature and the
equilibrium temperature of the print head during printing operations.
Hence, the degree of preheating may be varied in accordance with the
measured ambient temperature so as to provide for optimal results.

[0236]A simple operational schematic is illustrated in FIG. 17 with the
print head 130 including an on-board series of temperature sensors which
are connected to a temperature determination unit 131 for determining the
current temperature which in turn outputs to an ink ejection drive until
132 which determines whether preheating is required at any particular
stage. The on-chip (print head) temperature sensors can be simple MEMS
temperature sensors, the construction of which is well known to those
skilled in the art.

Manufacturing Process

[0237]IJ46 device manufacture can be constructed from a combination of
standard CMOS processing, and MEMS postprocessing. Ideally, no materials
should be used in the MEMS portion of the processing which are not
already in common use for CMOS processing. In the preferred embodiment,
the only MEMS materials are PECVD glass, sputtered TiN, and a sacrificial
material (which may be polyimide, PSG, BPSG, aluminum, or other
materials). Ideally, to fit corresponding drive circuits between the
nozzles without increasing chip area, the minimum process is a 0.5
micron, one poly, 3 metal CMOS process with aluminum metalization.
However, any more advanced process can be used instead. Alternatively,
NMOS, bipolar, BiCMOS, or other processes may be used. CMOS is
recommended only due to its prevalence in the industry, and the
availability of large amounts of CMOS fab capacity.

[0238]For a 100 mm photographic print head using the CMY process color
model, the CMOS process implements a simple circuit consisting of 19,200
states of shift register, 19,200 bits of transfer register, 19,200 enable
gates, and 19,200 drive transistors, There are also some clock buffers
and enable decoders. The clock speed of a photo print head is only 3.8
MHz, and a 30 ppm A4 print head is only 14 MHz, so the CMOS performance
is not critical. The CMOS process is fully completed, including
passivation and opening of bond pads before the MEMS processing begins.
This allows the CMOS processing to be completed in a standard CMOS fab,
with the MEMS processing being performed in a separate facility.

Reasons for Process Choices

[0239]It will be understood from those skilled in the art of manufacture
of MEMS devices that there are many possible process sequences for the
manufacture of an IJ46 print head. The process sequence described here is
based on a `generic` 0.5 micron (drawn) n-well CMOS process with 1 poly
and three metal layers. This table outlines the reasons for some of the
choices of this `nominal` process, to make it easier to determine the
effect of any alternative process choices.

TABLE-US-00001
Nominal Process Reason
CMOS Wide availability
0.5 micron or less 0.5 micron is required to fit drive electronics under
the
actuators
0.5 micron or Fully amortized fabs, low cost
more
N-well Performance of n-channel is more important than p-
channel transistors
6'' wafers Minimum practical for 4'' monilithic print heads
1 polysilicon 2 poly layers are not required, as there is little low
layer current connectivity
3 metal layers To supply high currents, most of metal 3 also provides
sacrificial structures
Aluminum Low cost, standard for 0.5 micron processes (copper
metalization may be more efficient)

[0241]Although many different CMOS and other processes can be used, this
process description is combined with an example CMOS process to show
where MEMS features are integrated in the CMOS masks, and show where the
CMOS process may be simplified due to the low CMOS performance
requirements.

Process steps described below are part of the example `generic` IP3M 0.5
micron CMOS process. [0242]1. As shown in FIG. 18, processing starts with
a standard 6'' p-type <100> wafers. (8'' wafers can also be used,
giving a substantial increase in primary yield). [0243]2. Using the
n-well mask of FIG. 19, implant the n-well transistor portions 210 of
FIG. 20. [0244]3. Grow a thin layer of SiO2 and deposit
Si3N4 forming a field oxide hard mask. [0245]4. Etch the
nitride and oxide using the active mask of FIG. 22. The mask is oversized
to allow for the LOCOS bird's beak. The nozzle chamber region is
incorporated in this mask, as field oxide is excluded from the nozzle
chamber. The result is a series of oxide regions 212, illustrated in FIG.
23. [0246]5. Implant the channel-stop using the n-well mask with a
negative resist, or using a complement of the n-well mask. [0247]6.
Perform any required channel stop implants as required by the CMOS
process used. [0248]7. Grow 0.5 micron of field oxide using LOCOS.
[0249]8. Perform any required n/p transistor threshold voltage
adjustments. Depending upon the characteristics of the CMOS process, it
may be possible to omit the threshold adjustments. This is because the
operating frequency is only 3.8 MHz, and the quality of the p-devices is
not critical. The n-transistor threshold is more significant, as the
on-resistance of the n-channel drive transistor has a significant effect
on the efficiency and power consumption while printing. [0250]9. Grow the
gate oxide. [0251]10. Deposit 0.3 microns of poly, and pattern using the
poly mask illustrated in FIG. 25 so as to form poly portions 214 shown in
FIG. 26. [0252]11. Perform the n+ implant shown e.g. 216 in FIG. 29 using
the n+ mask shown in FIG. 28. The use of a drain engineering processes
such as LDD should not be required, as the performance of the transistors
is not critical. [0253]12. Perform the p+ implant shown e.g. 218 in FIG.
32, using a complement of the n+ mask shown in FIG. 31, or using the n+
mask with a negative resist. The nozzle chamber region will be doped
either n+ or p+ depending upon whether it is included in the n+ mask or
not. The doping of this silicon region is not relevant as it is
subsequently etched, and the STS ASE etch process recommended does not
use boron as an etch stop. [0254]13. Deposit 0.6 microns of PECVD TEOS
glass to form ILD 1, shown e.g. 220 in FIG. 35. [0255]14. Etch the
contact cuts using the contact mask of FIG. 34. The nozzle region is
treated as a single large contact region, and will not pass typical
design rule checks. This region should therefore be excluded from the
DRC. [0256]15. Deposit 0.6 microns of aluminum to form metal 1. [0257]16.
Etch the aluminum using the metal 1 mask shown in FIG. 37 so as to form
metal regions e.g. 224 shown in FIG. 38. The nozzle metal region is
covered with metal 1 e.g. 225. This aluminum 225 is sacrificial, and is
etched as part of the MEMS sequence. The inclusion of metal 1 in the
nozzle is not essential, but helps reduce the step in the neck region of
the actuator lever arm. [0258]17. Deposit 0.7 microns of PECVD TEOS glass
to form ILD 2 regions e.g. 228 of FIG. 41. [0259]18. Etch the contact
cuts using the via 1 mask shown in FIG. 40. The nozzle region is treated
as a single large via region, and again it will not pass DRC. [0260]19.
Deposit 0.6 microns of aluminum to form metal 2. [0261]20. Etch the
aluminum using the metal 2 mask shown in FIG. 42 so as to form metal
portions e.g. 230 shown in FIG. 43. The nozzle region 231 is fully
covered with metal 2. This aluminum is sacrificial, and is etched as part
of the MEMS sequence. The inclusion of metal 2 in the nozzle is not
essential, but helps reduce the step in the neck region of the actuator
level arm. Sacrificial metal 2 is also used for another fluid control
feature. A relatively large rectangle of metal 2 is included in the neck
region 233 of the nozzle chamber. This is connected to the sacrificial
metal 3, so is also removed during the MEMS sacrificial aluminum etch.
The undercuts the lower rim of the nozzle chamber entrance for the
actuator (which is formed from ILD 3). The undercut adds 90 degrees to
angle of the fluid control surface, and thus increases the ability of
this rim to prevent ink surface spread. [0262]21. Deposit 0.7 microns of
PECVD TEOS glass to form ILD 3. [0263]22. Etch the contact cuts using the
via 2 mask shown in FIG. 45 so as to leave portions e.g. 236 shown in
FIG. 46. As well as the nozzle chamber, fluid control rims are also
formed in ILD 3. These will also not pass DRC. [0264]23. Deposit 1.0
microns of aluminum to form metal 3. [0265]24. Etch the aluminum using
the metal 3 mask shown in FIG. 47 so as to leave portions e.g. 238 as
shown in FIG. 48. Most of metal 3 e.g. 239 is a sacrificial layer used to
separate the actuator and paddle from the chip surface. Metal 3 is also
used to distribute V+ over the chip. The nozzle region is fully covered
with metal 3 e.g. 240. This aluminum is sacrificial, and is etched as
part of the MEMS sequence. The inclusion of metal 3 in the nozzle is not
essential, but helps reduce the step in the neck region of the actuator
lever arm. [0266]25. Deposit 0.5 microns of PECVD TEOS glass to form the
overglass. [0267]26. Deposit 0.5 microns of Si3N4 to form the
passivation layer. [0268]27. Etch the passivation and overglass using the
via 3 mask shown in FIG. 50 so as to form the arrangement of FIG. 51.
This mask includes access 242 the metal 3 sacrificial layer, and the vias
e.g. 243 to the heater actuator. Lithography of this step has 0.6 micron
critical dimensions (for the heater vias) instead of the normally relaxed
lithography used for opening bond pads. This is the one process step
which is different from the normal CMOS process flow. This step may
either be the last process step of the CMOS process, or the first step of
the MEMS process, depending upon the fab setup and transport
requirements. [0269]28. Wafer Probe. Much, but not all, of the
functionality of the chips can be determined at this stage. If more
complete testing at this stage is required, an active dummy load can be
included on chip for each drive transistor. This can be achieved with
minor chip area penalty, and allows complete testing of the CMOS
circuitry. [0270]29. Transfer the wafers from the CMOS facility to the
MEMS facility. These may be in the same fab, or may be distantly located.
[0271]30. Deposit 0.9 microns of magnetron sputtered TiN. Voltage is
-65V, magnetron current is 7.5 A, argon gas pressure is 0.3 Pa,
temperature is 300° C. This results in a coefficient of thermal
expansion of 9.4×10-6/° C., and a Young's modulus of
600 GPa [Thin Solid Films 270 p. 266, 1995], which are the key thin film
properties used. [0272]31. Etch the TiN using the heater mask shown in
FIG. 53. This mask defines the heater element, paddle arm, and paddle.
There is a small gap 247 shown in FIG. 54 between the heater and the TiN
layer of the paddle and paddle arm. This is to prevent electrical
connection between the heater and the ink, and possible electrolysis
problems. Sub-micron accuracy is required in this step to maintain a
uniformity of heater characteristics across the wafer. This is the main
reason that the heater is not etched simultaneously with the other
actuator layers. CD for the heater mask is 0.5 microns. Overlay accuracy
is +/-0.1 microns. The bond pads are also covered with this layer of TiN.
This is to prevent the bond pads being etched away during the sacrificial
aluminum etch. It also prevents corrosion of the aluminum bond pads
during operation. TiN is an excellent corrosion barrier for aluminum. The
resistivity of TiN is low enough to not cause problems with the bond pad
resistance. [0273]32. Deposit 2 microns of PECVD glass. This is
preferably done at around 350° C. to 400° C. to minimize
intrinsic stress in the glass. Thermal stress could be reduced by a lower
deposition temperature, however thermal stress is actually beneficial, as
the glass is sandwiched between two layers of TiN. The TiN/glass/TiN
tri-layer cancels bend due to thermal stress, and results in the glass
being under constant compressive stress, which increases the efficiency
of the actuator. [0274]33. Deposit 0.9 microns of magnetron sputtered
TiN. This layer is deposited to cancel bend from the differential thermal
stress of the lower TiN and glass layers, and prevent the paddle from
curling when released from the sacrificial materials. The deposition
characteristics should be identical to the first TiN layer. [0275]34.
Anisotropically plasma etch the TiN and glass using actuator mask as
shown in FIG. 56. This mask defines the actuator and paddle. CD for the
actuator mask is 1 micron. Overlay accuracy is +/-0.1 microns. The
results of the etching process is illustrated in FIG. 57 with the glass
layer 250 sandwiched between TiN layers 251,248. [0276]35. Electrical
testing can be performed by wafer probing at this time. All CMOS tests
and heater functionality and resistance tests can be completed at wafer
probe. [0277]36. Deposit 15 microns of sacrificial material. There are
many possible choices for this material. The essential requirements are
the ability to deposit a 15 micron layer without excessive wafer warping,
and a high etch selectivity to PECVD glass and TiN. Several possibilities
are phosphosilicate glass (PSG), borophosphosilicate glass (BPSG),
polymers such as polyimide, and aluminum. Either a close CTE match to
silicon (BPSG with the correct doping, filled polyimide) or a low Young's
modulus (aluminum) is required. This example uses BPSG. Of these issues,
stress is the most demanding due to the extreme layer thickness. BPSG
normally has a CTE well below that of silicon, resulting in considerable
compressive stress. However, the composition of BPSG can be varied
significantly to adjust its CTE close to that of silicon. As the BPSG is
a sacrificial layer, its electrical properties are not relevant, and
compositions not normally suitable as a CMOS dielectric can be used. Low
density, high porosity, and a high water content are all beneficial
characteristics as they will increase the etch selectivity versus PECVD
glass when using an anhydrous HF etch. [0278]37. Etch the sacrificial
layer to a depth of 2 microns using the nozzle mask as defined in FIG. 59
so as to form the structure 254 illustrated in section in FIG. 60. The
mask of FIG. 59 defines all of the regions where a subsequently deposited
overcoat is to be polished off using CMP. This includes the nozzles
themselves, and various other fluid control features. CD for the nozzle
mask is 2 microns. Overlay accuracy is +/-0.5 microns. [0279]38.
Anisotropically plasma etch the sacrificial layer down to the CMOS
passivation layer using the chamber mask as illustrated in FIG. 62. This
mask defines the nozzle chamber and actuator shroud including slots 255
as shown in FIG. 63. CD for the chamber mask is 2 microns, Overlay
accuracy is +/-0.2 microns. [0280]39. Deposit 0.5 microns of fairly
conformal overcoat material 257 as illustrated in FIG. 65. The electrical
properties of this material are irrelevant, and it can be a conductor,
insulator, or semiconductor. The material should be: chemically inert,
strong, highly selective etch with respect to the sacrificial material,
be suitable for CMP, and be suitable for conformal deposition at
temperatures below 500° C. Suitable materials include: PECVD
glass, MOCVD TiN, ECR CVD TiN, PECVD Si3N4, and many others.
The choice for this example is PECVD TEOS glass. This must have a very
low water content if BPSG is used as the sacrificial material and
anhydrous HF is used as the sacrificial etchant, as the anhydrous HF etch
relies on water content to achieve 1000:1 etch selectivity of BPSG over
TEOS glass. The confirmed overcoat 257 forms a protective covering shell
around the operational portions of the thermal bend actuator while
permitting movement of the actuator within the shell. [0281]40. Planarize
the wafer to a depth of 1 micron using CMP as illustrated in FIG. 67. The
CMP processing should be maintained to an accuracy of +/-0.5 microns over
the wafer surface. Dishing of the sacrificial material is not relevant.
This opens the nozzles 259 and fluid control regions e.g. 260. The
rigidity of the sacrificial layer relative to the nozzle chamber
structures during CMP is one of the key factors which may affect the
choice of sacrificial materials. [0282]41. Turn the print head wafer over
and securely mount the front surface on an oxidized silicon wafer blank
262 illustrated in FIG. 69 having an oxidized surface 263. The mounting
can be by way of glue 265. The blank wafers 262 can be recycled.
[0283]42. Thin the print head wafer to 300 microns using backgrinding (or
etch) and polish. The wafer thinning is performed to reduce the
subsequent processing duration for deep silicon etching from around 5
hours to around 2.5 hours. The accuracy of the deep silicon etch is also
improved, and the hard-mask thickness is halved to 2.6 microns. The
wafers could be thinned further to improve etch duration and print head
efficiency. The limitation to wafer thickness is the print head fragility
after sacrificial BPSG etch. [0284]43. Deposit a SiO2 hard mask (2.5
microns of PECVD glass) on the backside of the wafer and pattern using
the inlet mask as shown in FIG. 67. The hard mask of FIG. 67 is used for
the subsequent deep silicon etch, which is to a depth of 315 microns with
a hard mask selectivity of 150:1. This mask defines the ink inlets, which
are etched through the wafer. CD for the inlet mask is 4 microns. Overlay
accuracy is +/-2 microns. The inlet mask is undersize by 5.25 microns on
each side to allow for a re-entrant etch angle of 91 degrees over a 300
micron etch depth. Lithography for this step uses a mask aligner instead
of a stepper. Alignment is to patterns on the front of the wafer.
Equipment is readily available to allow sub-micron front-to-back
alignment. [0285]44. Back-etch completely through the silicon wafer
(using, for example, an ASE Advanced Silicon Etcher from Surface
Technology Systems) through the previously deposited hard mask. The STS
ASE is capable of etching highly accurate holes through the wafer with
aspect ratios of 30:1 and sidewalls of 90 degrees. In this case, a
re-entrant sidewall angle of 91 degrees is taken as nominal. A re-entrant
angle is chosen because the ASE performs better, with a higher etch rate
for a given accuracy, with a slightly re-entrant angle. Also, a
re-entrant etch can be compensated by making the holes on the mask
undersize. Non-re-entrant etch angles cannot be so easily compensated,
because the mask holes would merge. The wafer is also preferably diced by
this etch. The final result is as illustrated in FIG. 69 including back
etched ink channel portions 264. [0286]45. Etch all exposed aluminum.
Aluminum on all three layers is used as sacrificial layers in certain
places.

[0287]46. Etch all of the sacrificial material. The nozzle chambers are
cleared by this etch with the result being as shown in FIG. 71. If BPSG
is used as the sacrificial material, it can be removed without etching
the CMOS glass layers or the actuator glass. This can be achieved with
1000:1 selectivity against undoped glass such as TEOS, using anhydrous HF
at 1500 sccm in a N2 atmosphere at 60° C. [L. Chang et al,
"Anhydrous HF etch reduces processing steps for DRAM capacitors", Solid
State Technology Vol. 41 No. 5, pp 71-76, 1998]. The actuators are freed
and the chips are separated from each other, and from the blank wafer, by
this etch. If aluminum is used as the sacrificial layer instead of BPSG,
then its removal is combined with the previous step, and this step is
omitted. [0288]47. Pick up the loose print heads with a vacuum probe, and
mount the print heads in their packaging. This must be done carefully, as
the unpackaged print heads are fragile. The front surface of the wafer is
especially fragile, and should not be touched. This process should be
performed manually, as it is difficult to automate. The package is a
custom injection molded plastic housing incorporating ink channels that
supply the appropriate color ink to the ink inlets at the back of the
print head. The package also provides mechanical support to the print
head. The package is especially designed to place minimal stress on the
chip, and to distribute that stress evenly along the length of the
package. The print head is glued into this package with a compliant
sealant such as silicone. [0289]48. Form the external connections to the
print head chip. For a low profile connection with minimum disruption of
airflow, tape automated bonding (TAB) may be used. Wire bonding may also
be used if the printer is to be operated with sufficient clearance to the
paper. All of the bond pads are along one 100 mm edge of the chip. There
are a total of 504 bond pads, in 8 identical groups of 63 (as the chip is
fabricated using 8 stitched stepper steps). Each bond pad is
100×100 micron, with a pitch of 200 micron. 256 of the bond pads
are used to provide power and ground connections to the actuators, as the
peak current is 6.58 Amps at 3V. There are a total of 40 signal
connections to the entire print head (24 data and 16 control), which are
mostly bussed to the eight identical sections of the print head.
[0290]49. Hydrophobize the front surface of the print heads. This can be
achieved by the vacuum deposition of 50 nm or more of
polytetrafluoroethylene (PTFE). However, there are also many other ways
to achieve this. As the fluid is fully controlled by mechanical
protuberances formed in previous steps, the hydrophobic layer is an
`optional extra` to prevent ink spreading on the surface if the print
head becomes contaminated by dust. [0291]50. Plus the print heads into
their sockets. The socket provides power, data, and ink. The ink fills
the print-head by capillarity. Allow the completed print heads to fill
with ink, and test. FIG. 74 illustrates the filling of ink 268 into the
nozzle chamber.Process Parameters used for this Implementation Example

[0292]The CMOS process parameters utilized can be varied to suit any CMOS
process of 0.5 micron dimensions or better. The MEMS process parameters
should not be varied beyond the tolerances shown below. Some of these
parameters affect the actuator performance and fluidics, while others
have more obscure relationships. For example, the wafer thin stage
affects the cost and accuracy of the deep silicon etch, the thickness of
the back-side hard mask, and the dimensions of the associated plastic ink
channel molding. Suggested process parameters can be as follows:

[0293]Turning over to FIG. 76, there is illustrated the associated control
logic for a single ink jet nozzle. The control logic 280 is utilized to
activate a heater element 281 on demand. The control logic 280 includes a
shift register 282, a transfer register 283 and a firing control gate
284. The basic operation is to shift data from one shift register 282 to
the next until it is in place. Subsequently, the data is transferred to a
transfer register 283 upon activation of a transfer enable signal 286.
The data is latched in the transfer register 283 and subsequently, a
firing phase control signal 289 is utilized to activate a gate 284 for
output of a heating pulse to heat an element 281.

[0294]As the preferred implementation utilizes a CMOS layer for
implementation of all control circuitry, one form of suitable CMOS
implementation of the control circuitry will now be described. Turning
now to FIG. 77, there is illustrated a schematic block diagram of the
corresponding CMOS circuitry. Firstly, shift register 282 takes an
inverted data input and latches the input under control of shift clocking
signals 291, 292. The data input 290 is output 294 to the next shift
register and is also latched by a transfer register 283 under control of
transfer enable signals 296, 297. The enable gate 284 is activated under
the control of enable signal 299 so as to drive a power transistor 300
which allows for resistive heating of resistor 281. The functionality of
the shift register 282, transfer register 283 and enable gate 284 are
standard CMOS components well understood by those skilled in the art of
CMOS circuit design.

Replicated Units

[0295]The ink jet print head can consist of a large number of replicated
unit cells each of which has basically the same design. This design will
now be discussed.

[0296]Turning initially to FIG. 78, there is illustrated a general key or
legend of different material layers utilized in subsequent discussions.

[0297]FIG. 79 illustrates the unit cell 305 on a 1 micron grid 306. The
unit cell 305 is copied and replicated a large number of times with FIG.
79 illustrating the diffusion and poly-layers in addition to vias e.g.
308. The signals 290, 291, 292, 296, 297 and 299 are previously discussed
with reference to FIG. 77. A number of important aspects of FIG. 79
include the general layout including the shift register, transfer
register and gate and drive transistor. Importantly, the drive transistor
300 includes an upper poly-layer e.g. 309 which is laid out having a
large number of perpendicular traces e.g. 312. The perpendicular traces
are important in ensuring that the corrugated nature of a heater element
formed over the power transistor 300 will have a corrugated bottom with
corrugations running generally in the perpendicular direction of trace
112. This is best shown in FIGS. 69, 71 and 74. Consideration of the
nature and directions of the corrugations, which arise unavoidably due to
the CMOS wiring underneath, is important to the ultimate operational
efficiency of the actuator. In the ideal situation, the actuator is
formed without corrugations by including a planarization step on the
upper surface of the substrate step prior to forming the actuator.
However, the best compromise that obviates the additional process step is
to ensure that the corrugations extend in a direction that is transverse
to the bending axis of the actuator as illustrated in the examples, and
preferably constant along its length. This results in an actuator that
may only be 2% less efficient than a flat actuator, which in many
situations will be an acceptable result. By contrast, corrugations that
extend longitudinally would reduce the efficiency by about 20% compared
to a flat actuator.

[0298]In FIG. 80, there is illustrated the addition of the first level
metal layer which includes enable lines 296, 297.

[0299]In FIG. 81, there is illustrated the second level metal layer which
includes data in-line 290, SClock line 91, SClock 292, Q 294, TEn 296 and
TEn 297, V-320, VDD 321, VSS 322, in addition to associated
reflected components 323 to 328. The portions 330 and 331 are utilized as
a sacrificial etch.

[0300]Turning now to FIG. 82 there is illustrated the third level metal
layer which includes a portion 340 which is utilized as a sacrificial
etch layer underneath the heater actuator. The portion 341 is utilized as
part of the actuator structure with the portions 342 and 343 providing
electrical interconnections.

[0301]Turning now to FIG. 83, there is illustrated the planar conductive
heating circuit layer including heater arms 350 and 351 which are
interconnected to the lower layers. The heater arms are formed on either
side of a tapered slot so that they are narrower toward the fixed or
proximal end of the actuator arm, giving increased resistance and
therefore heating and expansion in that region. The second portion of the
heating circuit layer 352 is electrically isolated from the arms 350 and
351 by a discontinuity 355 and provides for structural support for the
main paddle 356. The discontinuity may take any suitable form but is
typically a narrow slot as shown at 355.

[0302]In FIG. 84 there is illustrated the portions of the shroud and
nozzle layer including shroud 353 and outer nozzle chamber 354.

[0303]Turning to FIG. 85, there is illustrated a portion 360 of a array of
ink ejection nozzles which are divided into three groups 361-363 with
each group providing separate color output, (cyan, magenta and yellow) so
as to provide full three color printing. A series of standard cell clock
buffers and address decoders 364 is also provided in addition to bond
pads 365 for interconnection with the external circuitry.

[0304]Each color group 361, 363 consists of two spaced apart rows of ink
ejection nozzles e.g. 367 each having a heater actuator element.

[0305]FIG. 87 illustrates one form of overall layout in a cut away manner
with a first area 370 illustrating the layers up to the polysilicon
level. A second area 371 illustrating the layers up to the first level
metal, the are 372 illustrating the layers up to the second level metal
and the area 373 illustrating the layers up to the heater actuator layer.

[0306]The ink ejection nozzles are grouped in two groups of 10 nozzles
sharing a common ink channel through the wafer. Turning to FIG. 88, there
is illustrated the back surface of the wafer which includes a series of
ink supply channels 380 for supplying ink to a front surface.

Replication

[0307]The unit cell is replicated 19,200 times on the 4'' print head, in
the hierarchy as shown in the replication hierarchy table below. The
layout grid is 1/21 at 0.5 micron (0.125 micron). Many of the ideal
transform distances fall exactly on a grid point. Where they do not, the
distance is rounded to the nearest grid point. The rounded numbers are
shown with an asterisk. The transforms are measured from the center of
the corresponding nozzles in all cases. The transform of a group of five
even nozzles into five odd nozzles also involves a 180° rotation.
The translation for this step occurs from a position where all five pairs
of nozzle centers are coincident.

[0308]Taking the example of a 4-inch print head suitable for use in camera
photoprinting as illustrated in FIG. 89, a 4-inch print head 380 consists
of 8 segments eg. 381, each segment is 1/2 an inch in length.
Consequently each of the segments prints bi-level cyan, magenta and
yellow dots over a different part of the page to produce the final image.
The positions of the 8 segments are shown in FIG. 89. In this example,
the print head is assumed to print dots at 1600 dpi, each dot is 15.875
microns in diameter. Thus each half-inch segment prints 800 dots, with
the 8 segments corresponding to positions as illustrated in the following
table:

[0309]Although each segment produces 800 dots of the final image, each dot
is represented by a combination of bi-level cyan, magenta, and yellow
ink. Because the printing is bi-level, the input image should be dithered
or error-diffused for best results.

[0310]Each segment 381 contains 2,400 nozzles: 800 each of cyan, magenta,
and yellow. A four-inch printhead contains 8 such segments for a total of
19,200 nozzles.

[0311]The nozzles within a single segment are grouped for reasons of
physical stability as well as minimization of power consumption during
printing. In terms of physical stability, as shown in FIG. 88 groups of
10 nozzles are grouped together and share the same ink channel reservoir.
In terms of power consumption, the groupings are made so that only 96
nozzles are fired simultaneously from the entire print head. Since the 96
nozzles should be maximally distant, 12 nozzles are fired from each
segment. To fire all 19,200 nozzles, 200 different sets of 96 nozzles
must be fired.

[0312]FIG. 90 shows schematically, a single pod 395 which consists of 10
nozzles numbered 1 to 10 sharing a common ink channel supply. 5 nozzles
are in one row, and 5 are in another. Each nozzle produces dots 15.875
μm in diameter. The nozzles are numbered according to the order in
which they must be fired.

[0313]Although the nozzles are fired in this order, the relationship of
nozzles and physical placement of dots on the printed page is different.
The nozzles from one row represent the even dots from one line on the
page, and the nozzles on the other row represent the odd dots from the
adjacent line on the page. FIG. 91 shows the same pod 395 with the
nozzles numbered according to the order in which they must be loaded.

[0314]The nozzles within a pod are therefore logically separated by the
width of 1 dot. The exact distance between the nozzles will depend on the
properties of the ink jet firing mechanism. In the best case, the print
head could be designed with staggered nozzles designed to match the flow
of paper. In the worst case there is an error of 1/3200 dpi. While this
error would be viewable under a microscope for perfectly straight lines,
it certainly will not be an apparent in a photographic image.

[0315]As shown in FIG. 92, three pods representing Cyan 398, Magenta 197,
and Yellow 396 units, are grouped into a tripod 400. A tripod represents
the same horizontal set of 10 dots, but on different lines. The exact
distance between different color pods depends on the ink jet operating
parameters, and may vary from one ink jet to another. The distance can be
considered to be a constant number of dot-widths, and must therefore be
taken into account when printing: the dots printed by the cyan nozzles
will be for different lines than those printed by the magenta or yellow
nozzles. The printing algorithm must allow for a variable distance up to
about 8 dot-widths.

[0316]As illustrated in FIG. 93, 10 tripods eg. 404 are organized into a
single podgroup 405. Since each tripod contains 30 nozzles, each podgroup
contains 300 nozzles: 100 cyan, 100 magenta and 100 yellow nozzles. The
arrangement is shown schematically in FIG. 93, with tripods numbered 0-9.
The distance between adjacent tripods is exaggerated for clarity.

[0317]As shown in FIG. 94, two podgroups (PodgroupA 410 and PodgroupB 411)
are organized into a single firegroup 414, with 4 firegroups in each
segment 415. Each segment 415 contains 4 firegroups. The distance between
adjacent firegroups is exaggerated for clarity.

[0318]The print head contains a total of 19,200 nozzles. A Print Cycle
involves the firing of up to all of these nozzles, dependent on the
information to be printed. A Load Cycle involves the loading up of the
print head with the information to be printed during the subsequent Print
Cycle.

[0319]Each nozzle has an associated NozzleEnable (289 of FIG. 76) bit that
determines whether or not the nozzle will fire during the Print Cycle.
The NozzleEnable bits (one per nozzle) are loaded via a set of shift
registers.

[0320]Logically there are 3 shift registers per color, each 800 deep. As
bits are shifted into the shift register they are directed to the lower
and upper nozzles on alternate pulses. Internally, each 800-deep shift
register is comprised of two 400-deep shift registers: one for the upper
nozzles, and one for the lower nozzles. Alternate bits are shifted into
the alternate internal registers. As far as the external interface is
concerned however, there is a single 800 deep shift register.

[0321]Once all the shift registers have been fully loaded (800 pulses),
all of the bits are transferred in parallel to the appropriate
NozzleEnable bits. This equates to a single parallel transfer of 19,200
bits. Once the transfer has taken place, the Print Cycle can begin. The
Print Cycle and the Load Cycle can occur simultaneously as long as the
parallel load of all NozzleEnable bits occurs at the end of the Print
Cycle.

[0322]In order to print a 6''×4'' image at 1600 dpi in say 2
seconds, the 4'' print head must print 9,600 lines (6×1600).
Rounding up to 10,000 lines in 2 seconds yields a line time of 200
microseconds. A single Print Cycle and a single Load Cycle must both
finish within this time. In addition, a physical process external to the
print head must move the paper an appropriate amount.

Load Cycle

[0323]The Load Cycle is concerned with loading the print head's shift
registers with the next Print Cycle's NozzleEnable bits.

[0324]Each segment has 3 inputs directly related to the cyan, magenta, and
yellow pairs of shift registers. These inputs are called CDataIn,
MDataIn, and YDataIn. Since there are 8 segments, there are a total of 24
color input lines per print head. A single pulse on the SRClock line
(shared between all 8 segments) transfers 24 bits into the appropriate
shift registers. Alternate pulses transfer bits to the lower and upper
nozzles respectively. Since there are 19,200 nozzles, a total of 800
pulses are required for the transfer. Once all 19,200 bits have been
transferred, a single pulse on the shared PTransfer line causes the
parallel transfer of data from the shift registers to the appropriate
NozzleEnable bits. The parallel transfer via a pulse on PTransfer must
take place after the Print Cycle has finished. Otherwise the NozzleEnable
bits for the line being printed will be incorrect.

[0325]Since all 8 segments are loaded with a single SRClock pulse, the
printing software must produce the data in the correct sequence for the
print head. As an example, the first SRClock pulse will transfer the C,
M, and Y bits for the next Print Cycle's dot 0, 800, 1600, 2400, 3200,
4000, 4800, and 5600. The second SRClock pulse will transfer the C, M,
and Y bits for the next Print Cycle's dot 1, 801, 1601, 2401, 3201, 4001,
4801 and 5601. After 800 SRClock pulses, the Ptransfer pulse can be
given.

[0326]It is important to note that the odd and even C, M, and Y outputs,
although printed during the same Print Cycle, do not appear on the same
physical output line. Thy physical separation of odd and even nozzles
within the print head, as well as separation between nozzles of different
colors ensures that they will produce dots on different lines of the
page. This relative difference must be accounted for when loading the
data into the print head. The actual difference in lines depends on the
characteristics of the ink jet used in the print head. The differences
can be defined by variables D1 and D2 where D1 is the
distance between nozzles of different colors (likely value 4 to 8), and
D2 is the distance between nozzles of the same color (likely
value=1). Table 3 shows the dots transferred to segment n of a print head
on the first 4 pulses.

[0327]And so on for all 800 pulses. The 800 SRClock pulses (each clock
pulse transferring 24 bits) must take place within the 200 microseconds
line time. Therefore the average time to calculate the bit value for each
of the 19, 200 nozzles must not exceed 200 microseconds/19200=10
nanoseconds. Data can be clocked into the print head at a maximum rate of
10 MHz, which will load the data in 80 microseconds. Clocking the data in
at 4 MHz will load the data in 200 microseconds.

Print Cycle

[0328]The print head contains 19,200 nozzles. To fire them all at once
would consume too much power and be problematic in terms of ink refill
and nozzle interference. A single print cycle therefore consists of 200
different phases. 96 maximally distant nozzles are fired in each phase,
for a total of 19,200 nozzles.

[0329]4 bits TripodSelect (select 1 of 10 tripods from a firegroup)

[0330]The 96 nozzles fired each round equate to 12 per segment (since all
segments are wired up to accept the same print signals). The 12 nozzles
from a given segment come equally from each firegroup. Since there are 4
firegroups, 3 nozzles fire from each firegroup. The 3 nozzles are one per
color. The nozzles are determined by:

[0331]4 bits NozzleSelect (select 1 of 10 nozzles from a pod)

[0332]The duration of the firing pulse is given by the AEnable and BEnable
lines, which fire the PodgroupA and PodgroupB nozzles from all firegroups
respectively. The duration of a pulse depends on the viscosity of the ink
(dependent on temperature and ink characteristics) and the amount of
power available to the print head. The AEnable and BEnable are separate
lines in order that the firing pulses can overlap. Thus the 200 phases of
a Print Cycle consist of 100 A phases and 100 B phases, effectively
giving 100 sets of Phase A and Phase B.

[0333]When a nozzle fires, it takes approximately 100 microseconds to
refill. This is not a problem since the entire Print Cycle takes 200
microseconds. The firing of a nozzle also causes perturbations for a
limited time within the common ink channel of that nozzle's pod. The
perturbations can interfere with the firing of another nozzle within the
same pod. Consequently, the firing of nozzles within a pod should be
offset by at least this amount. The procedure is to therefore fire three
nozzles from a tripod (one nozzle per color) and then move onto the next
tripod within the podgroup. Since there are 10 tripods in a given
podgroup, 9 subsequent tripods must fire before the original tripod must
fire its next three nozzles. The 9 firing intervals of 2 microseconds
gives an ink settling time of 18 microseconds. [0334]Consequently, the
firing order is: [0335]TripodSelect 0, NozzleSelect 0 (Phases A and B)
[0336]TripodSelect 1, NozzleSelect 0 (Phases A and B) [0337]TripodSelect
2, NozzleSelect 0 (Phases A and B) [0338]. . . [0339]TripodSelect 9,
NozzleSelect 0 (Phases A and B) [0340]TripodSelect 0, NozzleSelect 1
(Phases A and B) [0341]TripodSelect 1, NozzleSelect 1 (Phases A and B)
[0342]TripodSelect 2, NozzleSelect 1 (Phases A and B) [0343]. . .
[0344]TripodSelect 8, NozzleSelect 9, Phases A and B) [0345]TripodSelect
9, NozzleSelect 9 (Phases A and B)

[0346]Note that phases A and B can overlap. The duration of a pulse will
also vary due to battery power and ink viscosity (which changes with
temperature). FIG. 95 shows the AEnable and BEnable lines during a
typical Print Cycle.

Feedback from the Print Head

[0347]The print head produces several lines of feedback (accumulated from
the 8 segments). The feedback lines can be used to adjust the timing of
the firing pulses. Although each segment produces the same feedback, the
feedback from all segments share the same tri-state bus lines.
Consequently only one segment at a time can provide feedback. A pulse on
the SenseEnable line ANDed with data on CYAN enables the sense lines for
that segment. The feedback sense lines are as follows:

[0348]Tsense informs the controller how hot the print head is. This allows
the controller to adjust timing of firing pulses, since temperature
affects the viscosity of the ink.

[0349]Vsense informs the controller how much voltage is available to the
actuator. This allows the controller to compensate for a flat battery or
high voltage source by adjusting the pulse width.

[0350]Rsense_informs the controller of the resistivity (Ohms per square)
of the actuator heater. This allows the controller to adjust the pulse
widths to maintain a constant energy irrespective of the heater
sensitivity.

[0351]Wsense informs the controller of the width of the critical part of
the heater, which may vary up to ±5% due to lithographic and etching
variations. This allows the controller to adjust the pulse width
appropriately.

Preheat Mode

[0352]The printing process has a strong tendency to stay at the
equilibrium temperature. To ensure that the first section of the printed
photograph has a consistent dot size, ideally the equilibrium temperature
should be met before printing any dots. This is accomplished via a
preheat mode.

[0353]The Preheat mode involves a single Load Cycle to all nozzles with 1s
(i.e. setting all nozzles to fire), and a number of short firing pulses
to each nozzle. The duration of the pulse must be insufficient to fire
the drops, but enough to heat up the ink surrounding the heaters.
Altogether about 200 pulses for each nozzles are required, cycling
through in the same sequence as a standard Print Cycle.

[0354]Feedback during the Preheat mode is provided by Tsense, and
continues until an equilibrium temperature is reached (about 30°
C. above ambient). The duration of the Preheat mode can be around 50
milliseconds, and can be tuned in accordance with the ink composition.

[0356]Internal to the print head, each segment has the following
connections to the bond pads:

PadConnections

[0357]Although an entire print head has a total of 504 connections, the
mask layout contains only 63. This is because the chip is composed of
eight identical and separate sections, each 12.7 micron long. Each of
these sections has 63 pads at a pitch of 200 microns. There is an extra
50 microns at each end of the group of 63 pads, resulting in an exact
repeat distance of 12,700 microns (12.7 micron, 1/2'')

[0360]The main consequence of a change in ambient temperature is that the
ink viscosity and surface tension changes. As the bend actuator responds
only to differential temperature between the actuator layer and the bend
compensation layer, ambient temperature has negligible direct effect on
the bend actuator. The resistivity of the TiN heater changes only
slightly with temperature. The following simulations are for an water
based ink, in the temperature range 0° C. to 80° C.

[0361]The drop velocity and drop volume does not increase monotonically
with increasing temperature as one may expect. This is simply explained:
as the temperature increases, the viscosity falls faster than the surface
tension falls. As the viscosity falls, the movement of ink out of the
nozzle is made slightly easier. However, the movement of the ink around
the paddle--from the high pressure zone at the paddle front to the low
pressure zone behind the paddle--changes even more. Thus more of the ink
movement is `short circuited` at higher temperatures and lower
viscosities.

[0362]The temperature of the IJ46 print head is regulated to optimize the
consistency of drop volume and drop velocity. The temperature is sensed
on chip for each segment. The temperature sense signal (Tsense) is
connected to a common Tsense output. The appropriate Tsense signal is
selected by asserting the Sense Enable (Sen) and selecting the
appropriate segment using the D[C0.7] lines. The Tsense signal is
digitized by the drive ASIC, and drive pulse width is altered to
compensate for the ink viscosity change. Data specifying the
viscosity/temperature relationship of the ink is stored in the
Authentication chip associated with the ink.

Variation with Nozzle Radius

[0363]The nozzle radius has a significant effect on the drop volume and
drop velocity. For this reason it is closely controlled by 0.5 micron
lithography. The nozzle is formed by a 2 micron etch of the sacrificial
material, followed by deposition of the nozzle wall material and a CMP
step. The CMP planarizes the nozzle structures, removing the top of the
overcoat, and exposed the sacrificial material inside. The sacrificial
material is subsequently removed, leaving a self-aligned nozzle and
nozzle rim. The accuracy internal radius of the nozzle is primarily
determined by the accuracy of the lithography, and the consistency of the
sidewall angle of the 2 micron etch.

[0364]The following table shows operation at various nozzle radii. With
increasing nozzle radius, the drop velocity steadily decreases. However,
the drop volume peaks at around a 5.5 micron radius. The nominal nozzle
radius is 5.5 microns, and the operating tolerance specification allows a
4% variation on this radius, giving a range of 5.3 to 5.7 microns. The
simulations also include extremes outside of the nominal operating range
(5.0 and 6.0 micron). The major nozzle radius variations will likely be
determined by a combination of the sacrificial nozzle etch and the CMP
step. This means that variations are likely to be non-local: differences
between wafers, and differences between the center and the perimeter of a
wafer. The between wafer differences are compensated by the `brightness`
adjustment. Within wafer variations will be imperceptible as long as they
are not sudden.

[0365]A print head constructed in accordance with the aforementioned
techniques can be utilized in a print camera system similar to that
disclosed in PCT patent application No. PCT/AU98/00544. A print head and
ink supply arrangement suitable for utilization in a print on demand
camera system will now be described. Starting initially with FIG. 96 and
FIG. 97, there is illustrated portions of an ink supply arrangement in
the form of an ink supply unit 430. The supply unit can be configured to
include three ink storage chambers 521 to supply three color inks to the
back surface of a print head, which in the preferred form is a print head
chip 431. The ink is supplied to the print head by means of an ink
distribution molding or manifold 433 which includes a series of slots
e.g. 434 for the flow of ink via closely toleranced ink outlets 432 to
the back of the print head 431. The outlets 432 are very small having a
width of about 100 microns and accordingly need to be made to a much
higher degree of accuracy than the adjacent interacting components of the
ink supply unit such as the housing 495 described hereafter.

[0366]The print head 431 is of an elongate structure and can be attached
to the print head aperture 435 in the ink distribution manifold by means
of silicone gel or a like resilient adhesive 520.

[0367]Preferably, the print head is attached along its back surface 438
and sides 439 by applying adhesive to the internal sides of the print
head aperture 435. In this manner the adhesive is applied only to the
interconnecting faces of the aperture and print head, and the risk of
blocking the accurate ink supply passages 380 formed in the back of the
print head chip 431 (see FIG. 88) is minimised. A filter 436 is also
provided that is designed to fit around the distribution molding 433 so
as to filter the ink passing through the molding 433.

[0368]Ink distribution molding 433 and filter 436 are in turn inserted
within a baffle unit 437 which is again attached by means of a silicone
sealant applied at interface 438, such that ink is able to, for example,
flow through the holes 440 and in turn through the holes 434. The baffles
437 can be a plastic injection molded unit which includes a number of
spaced apart baffles or slats 441-443. The baffles are formed within each
ink channel so as to reduce acceleration of the ink in the storage
chambers 521 as may be induced by movement of the portable printer, which
in this preferred form would be most disruptive along the longitudinal
extent of the print head, whilst simultaneously allowing for flows of ink
to the print head in response to active demand therefrom. The baffles are
effective in providing for portable carriage of the ink so as to minimize
disruption to flow fluctuations during handling.

[0369]The baffle unit 437 is in turn encased in a housing 445. The housing
445 can be ultrasonically welded to the baffle member 437 so as to seal
the baffle member 437 into three separate ink chambers 521. The baffle
member 437 further includes a series of pierceable end wall portions
450-452 which can be pierced by a corresponding mating ink supply conduit
for the flow of ink into each of the three chambers. The housing 445 also
includes a series of holes 455 which are hydrophobically sealed by means
of tape or the like so as to allow air within the three chambers of the
baffle units to escape whilst ink remains within the baffle chambers due
to the hydrophobic nature of the holes eg. 455.

[0370]By manufacturing the ink distribution unit in separate interacting
components as just described, it is possible to use relatively
conventional molding techniques, despite the high degree of accuracy
required at the interface with the print head. That is because the
dimensional accuracy requirements are broken down in stages by using
successively smaller components with only the smallest final member being
the ink distribution manifold or second member needing to be produced to
the narrower tolerances needed for accurate interaction with the ink
supply passages 380 formed in the chip.

[0371]The housing 445 includes a series of positioning protuberances eg.
460-462. A first series of protuberances is designed to accurately
position interconnect means in the form of a tape automated bonded film
470, in addition to first 465 and second 466 power and ground busbars
which are interconnected to the TAB film 470 at a large number of
locations along the surface of the TAB film so as to provide for low
resistance power and ground distribution along the surface of the TAB
film 470 which is in turn interconnected to the print head chip 431.

[0372]The TAB film 470, which is shown in more detail in an opened state
in FIGS. 102 and 103, is double sided having on its outer side a
data/signal bus in the form of a plurality of longitudinally extending
control line interconnects 550 which releasably connect with a
corresponding plurality of external control lines. Also provided on the
outer side are busbar contacts in the form of deposited noble metal
strips 552.

[0373]The inner side of the TAB film 470 has a plurality of transversely
extending connecting lines 553 that alternately connect the power supply
via the busbars and the control lines 550 to bond pads on the print head
via region 554. The connection with the control lines occurring by means
of vias 556 that extend through the TAB film. One of the many advantages
of using the TAB film is providing a flexible means of connecting the
rigid busbar rails to the fragile print head chip 431.

[0374]The busbars 465, 466 are in turn connected to contacts 475, 476
which are firmly clamped against the busbars 465, 466 by means of cover
unit 478. The cover unit 478 also can comprise an injection molded part
and includes a slot 480 for the insertion of an aluminum bar for
assisting in cutting a printed page.

[0375]Turning now to FIG. 98 there is illustrated a cut away view of the
print head unit 430, associated platen unit 490, print roll and ink
supply unit 491 and drive power distribution unit 492 which interconnects
each of the units 430, 490 and 491.

[0376]The guillotine blade 495 is able to be driven by a first motor along
the aluminum blade 498 so as to cut a picture 499 after printing has
occurred. The operation of the system of FIG. 98 is very similar to that
disclosed in PCT patent application PCT/AU98/00544. Ink is stored in the
core portion 500 of a print roll former 501 around which is rolled print
media 502. The print media is fed under the control of electric motor 494
between the platen 290 and print head unit 490 with the ink being
interconnected via ink transmission channels 505 to the print head unit
430. The print roll unit 491 can be as described in the aforementioned
PCT specification. In FIG. 99, there is illustrated the assembled form of
single printer unit 510.

Features and Advantages

[0377]The IJ46 print head has many features and advantages over other
printing technologies. In some cases, these advantages stem from new
capabilities. In other cases, the advantages stem from the avoidance of
problems inherent in prior art technologies. A discussion of some of
these advantages follows.

High Resolution

[0378]The resolution of a IJ46 print head is 1,600 dots per inch (dpi) in
both the scan direction and transverse to the scan direction. This allows
full photographic quality color images, and high quality text (including
Kanji). Higher resolutions are possible: 2,400 dpi and 4,800 dpi versions
have been investigated for special applications, but 1,600 dpi is chosen
as ideal for most applications. The true resolution of advanced
commercial piezoelectric devices is around 120 dpi and thermal ink jet
devices around 600 dpi.

Excellent Image Quality

[0379]High image quality requires high resolution and accurate placement
of drops. The monolithic page width nature of IJ46 print heads allows
drop placement to sub-micron precision. High accuracy is also achieved by
eliminating misdirected drops, electrostatic deflection, air turbulence,
and eddies, and maintaining highly consistent drop volume and velocity.
Image quality is also ensured by the provision of sufficient resolution
to avoid requiring multiple ink densities. Five color or 6 color `photo`
ink jet systems can introduce halftoning artifacts in mid tones (such as
flesh-tones) if the dye interaction and drop sizes are not absolutely
perfect. This problem is eliminated in binary three color systems such as
used in IJ46 print heads.

High Speed (30 ppm Per Print Head)

[0380]The page width nature of the print head allows high-speed operation,
as no scanning is required. The time to print a full color A4 page is
less than 2 seconds, allowing full 30 page per minute (ppm) operation per
print head. Multiple print heads can be used in parallel to obtain 60
ppm. 90 ppm, 120 ppm, etc. IJ46 print heads are low cost and compact, so
multiple head designs are practical.

Low Cost

[0381]As the nozzle packing density of the IJ46 print head is very high,
the chip area per print head can be low. This leads to a low
manufacturing cost as many print head chips can fit on the same wafer.

All Digital Operation

[0382]The high resolution of the print head is chosen to allow fully
digital operation using digital halftoning. This eliminates color
non-linearity (a problem with continuous tone printers), and simplifies
the design of drive ASICs.

[0384]As the drop ejector is a precise mechanical mechanism, and does not
rely on bubble nucleation, accurate drop velocity control is available.
This allows low drop velocities (3-4 m/s) to be used in applications
where media and airflow can be controlled. Drop velocity can be
accurately varied over a considerable range by varying the energy
provided to the actuator. High drop velocities (10 to 15 m/s) suitable
for plan-paper operation and relatively uncontrolled conditions can be
achieved using variations of the nozzle chamber and actuator dimensions.

Fast Drying

[0385]A combination of very high resolution, very small drops, and high
dye density allows full color printing with much less water ejected. A
1600 dpi IJ46 print head ejects around 33% of the water of a 600 dpi
thermal ink jet printer. This allows fast drying and virtually eliminates
paper cockle.

Wide Temperature Range

[0386]IJ46 print heads are designed to cancel the effect of ambient
temperature. Only the change in ink characteristics with temperature
affects operation and this can be electronically compensated. Operating
temperature range is expected to be 0° C. to 50° C. for
water based inks.

No Special Manufacturing Equipment Required

[0387]The manufacturing process for IJ46 print heads leverages entirely
from the established semiconductor manufacturing industry. Most ink jet
systems encounter major difficulty and expense in moving from the
laboratory to production, as high accuracy specialized manufacturing
equipment is required.

High Production Capacity Available

[0388]A 6'' CMOS fab with 10,000 wafer starts per month can produce around
18 million print heads per annum. An 8'' CMOS fab with 20,000 wafer
starts per month can produce around 60 million print heads per annum.
There are currently many such CMOS fabs in the world.

Low Factory Setup Cost

[0389]The factory set-up cost is low because existing 0.5 micron 6'' CMOS
fabs can be used. These fabs could be fully amortized, and essentially
obsolete for CMOS logic production. Therefore, volume production can use
`old` existing facilities. Most of the MEMS post-processing can also be
performed in the CMOS fab.

Good Light-Fastness

[0390]As the ink is not heated, there are few restrictions on the types of
dyes that can be used. This allows dyes to be chosen for optimum
light-fastness. Some recently developed dyes from companies such as
Avecia and Hoechst have light-fastness of 4. This is equal to the
light-fastness of many pigments, and considerably in excess of
photographic dyes and of ink jet dyes in use until recently.

Good Water-Fastness

[0391]As with light-fastness, the lack of thermal restrictions on the dye
allows selection of dyes for characteristics such as water-fastness. For
extremely high water-fastness (as is required for washable textiles)
reactive dyes can be used.

Excellent Color Gamut

[0392]The use of transparent dyes of high color purity allows a color
gamut considerably wider than that of offset printing and silver halide
photography. Offset printing in particular has a restricted gamut due to
light scattering from the pigments used. With three-color systems (CMY)
or four-color systems (CMYK) the gamut is necessarily limited to the
tetrahedral volume between the color vertices. Therefore it is important
that the cyan, magenta and yellow dies are as spectrally pure as
possible. A slightly wide `hexcone` gamut that includes pure reds,
greens, and blues can be achieved using a 6 color (CMYRGB) model. Such a
six color print head can be made economically as it requires a chip width
of only 1 mm.

Elimination of Color Bleed

[0393]Ink bleed between colors occurs if the different primary colors are
printed while the previous color is wet. While image blurring due to ink
bleed is typically insignificant at 1600 dpi, ink bleed can `muddy` the
midtones of an image. Ink bleed can be eliminated by using
microemulsion-based ink, for which IJ46 print heads are highly suited.
The use of microemulsion ink can also help prevent nozzle clogging and
ensure long-term ink stability.

High Nozzle Count

[0394]An IJ46 print head has 19,200 nozzles in a monolithic CMY
three-color photographic print head. While this is large compared to
other print heads, it is a small number compared to the number of devices
routinely integrated on CMOS VLSI chips in high volume production. It is
also less than 3% of the number of movable mirrors which Texas
Instruments integrates in its Digital Micromirror Device (DMD),
manufactured using similar CMOS and MEMS processes.

51,200 Nozzles Per A4 Page Width Print Head

[0395]A four color (CMYK) IJ46 print head for page width A4/US letter
printing uses two chips. Each 0.66 cm2 chip has 25,600 nozzles for a
total of 51,200 nozzles.

Integration of Drive Circuits

[0396]In a print head with as many as 51,200 nozzles, it is essential ti
integrate data distribution circuits (shift registers), data timing, and
drive transistors with the nozzles. Otherwise, a minimum of 51,201
external connections would be required. This is a severe problem with
piezoelectric ink jets, as drive circuits cannot be integrated on
piezoelectric substrates. Integration of many millions of connections is
common in CMOS VLSI chips, which are fabricated in high volume at high
yield. It is the number of off-chip connections that must be limited.

Monolithic Fabrication

[0397]IJ46 print heads are made as a single monolithic CMOS chip, so no
precision assembly is required. All fabrication is performed using
standard CMOS VLSI and MEMS (Micro-Electro-Mechanical Systems) processes
and materials. In thermal ink jet and some piezoelectric ink jet systems,
the assembly of nozzle plates with the print head chip is a major cause
of low yields, limited resolution, and limited size. Also, page width
arrays are typically constructed from multiple smaller chips. The
assembly and alignment of these chips is an expensive process.

Modular, Extendable for Wide Print Widths

[0398]Long page width print heads can be constructed by butting two or
more 100 mm IJ46 print heads together. The edge of the IJ46 print head
chip is designed to automatically align to adjacent chips. One print head
gives a photographic size printer, two gives an A4 printer, and four
gives an A3 printer. Larger numbers can be used for high speed digital
printing, page width wide format printing, and textile printing.

Duplex Operation

[0399]Duplex printing at the full print speed is highly practical. The
simplest method is to provide two print heads--one on each side of the
paper. The cost and complexity of providing two print heads is less than
that of mechanical systems to turn over the sheet of paper.

Straight Paper Path

[0400]As there are no drums required, a straight paper path can be used to
reduce the possibility of paper jams. This is especially relevant for
office duplex printers, where the complex mechanisms required to turn
over the pages are a major source of paper jams.

High Efficiency

[0401]Thermal ink jet print heads are only around 0.01% efficient
(electrical energy input compared to drop kinetic energy and increased
surface energy). IJ46 print heads are more than 20 times as efficient.

Self-Cooling Operation

[0402]The energy required to eject each drop is 160 nJ (0.16 microJoules),
a small fraction of that required for thermal ink jet printers. The low
energy allows the print head to be completely cooled by the ejected ink,
with only a 40° C. worst-case ink temperature rise. No heat
sinking is required.

Low Pressure

[0403]The maximum pressure generated in an IJ46 print head is around 60
kPa (0.6 atmospheres). The pressures generated by bubble nucleation and
collapse in thermal ink jet and Bubblejet systems are typically in excess
of 10 Mpa (100 atmospheres), which is 160 times the maximum IJ46 print
head pressure. The high pressures in Bubblejet and thermal ink jet
designs result in high mechanical stresses.

Low Power

[0404]A 30 ppm A4 IJ46 print head requires about 67 Watts when printing
full 3 color black. When printing 5% coverage, average power consumption
is only 3.4 Watts.

Low Voltage Operation

[0405]IJ46 print heads can operate from a single 3V supply, the same as
typical drive ASICs. Thermal ink jets typically require at least 20 V,
and piezoelectric ink jets often require more than 50 V. The IJ46 print
head actuator is designed for nominal operation at 2.8 volts, allowing a
0.2 volt drop across the drive transistor, to achieve 3V chip operation.

Operation from 2 or 4 AA Batteries

[0406]Power consumption is low enough that a photographic IJ46 print head
can operate from AA batteries. A typical 6''×4'' photograph
requires less than 20 Joules to print (including drive transistor
losses). Four AA batteries are recommended if the photo is to be printed
in 2 seconds. If the print time is increased to 4 seconds, 2 AA batteries
can be used.

Battery Voltage Compensation

[0407]IJ46 print heads can operate from an unregulated battery supply, to
eliminate efficiency losses of a voltage regulator. This means that
consistent performance must be achieved over a considerable range of
supply voltages. The IJ46 print head senses the supply voltage, and
adjusts actuator operation to achieve consistent drop volume.

Small Actuator and Nozzle Area

[0408]The area required by an IJ46 print head nozzle, actuator, and drive
circuit is 1764 μm2. This is less than 1% of the area required by
piezoelectric ink jet nozzles, and around 5% of the area required by
Bubblkejet nozzles. The actuator area directly affects the print head
manufacturing cost.

Small Total Print Head Size

[0409]An entire print head assembly (including ink supply channels) for an
A4, 30 ppm, 1,600 dpi, four color print head is 210 mm×12
mm×7 mm. The small size allows incorporation into notebook
computers and miniature printers. A photograph printer is 106 mm×7
mm×7 mm, allowing inclusion in pocket digital cameras, palmtop
PC's, mobile phone/fax, and so on. Ink supply channels take most of this
volume. The print head chip itself is only 102 mm×0.55 mm×0.3
mm.

Miniature Nozzle Capping System

[0410]A miniature nozzle capping system has been designed for IJ46 print
heads. For a photograph printer this nozzle capping system is only 106
mm×5 mm×4 mm, and does not require the print head to move.

High Manufacturing Yield

[0411]The projected manufacturing yield (at maturity) of the IJ46 print
heads is at least 80%, as it is primarily a digital CMOS chip with an
area of only 0.55 cm2. Most modern CMOS processes achieve high yield
with chip areas in excess of 1 cm2. For chips less than around 1
cm2, cost is roughly proportional to chip area. Cost increases
rapidly between 1 cm2 and 4 cm2, with chips larger than this
rarely being practical. There is a strong incentive to ensure that the
chip area is less than 1 cm2. For thermal ink jet and Bubblejet
print heads, the chip width is typically around 5 mm, limiting the cost
effective chip length to around 2 cm. A major target of IJ46 print head
development has been to reduce the chip width as much as possible,
allowing cost effective monolithic page width print heads.

Low Process Complexity

[0412]With digital IC manufacture, the mask complexity of the device has
little or no effect on the manufacturing cost or difficulty. Cost is
proportional to the number of process steps, and the lithographic
critical dimensions. IJ46 print heads use a standard 0.5 micron single
poly triple metal CMOS manufacturing process, with an additional 5 MEMS
mask steps. This makes the manufacturing process less complex than a
typical 0.25 micron CMOS logic process with 5 level metal.

Simple Testing

[0413]IJ46 print heads include test circuitry that allows most testing to
be completed at the wafer probe state. Testing of all electrical
properties, including the resistance of the actuator, can be completed at
this stage. However, actuator motion can only be tested after release
from the sacrificial materials, so final testing must be performed on the
packaged chips.

Low Cost Packaging

[0414]IJ46 print heads are packaged in an injection molded polycarbonate
package. All connections are made using Tape Automated Bonding (TAB)
technology (though wire bonding can be used as an option). All
connections are along one edge of the chip.

No Alpha Particle Sensitivity

[0415]Alpha particle emission does not need to be considered in the
packaging, as there are no memory elements except static registers, and a
change of state due to alpha particle tracks is likely to cause only a
single extra dot to be printed (or not) on the paper.

Relaxed Critical Dimensions

[0416]The critical dimension (CD) of the IJ46 print head CMOS drive
circuitry is 0.5 microns. Advanced digital IC's such as microprocessors
currently use CDs of 0.25 microns, which is two device generations more
advanced than the IJ46 print head requires. Most of the MEMS post
processing steps have CDs of 1 micron or greater.

Low Stress during Manufacture

[0417]Devices cracking during manufacture are a critical problem with both
thermal ink jet and piezoelectric devices. This limits the size of the
print head that it is possible to manufacture. The stresses involved in
the manufacture of IJ46 print heads are no greater than those required
for CMOS fabrication.

No Scan Banding

[0418]IJ46 print heads are full page width, so do not scan. This
eliminates one of the most significant image quality problems of ink jet
printers. Banding due to other causes (mis-directed drops, print head
alignment) is usually a significant problem in page width print heads.
These causes of banding have also been addressed.

`Perfect` Nozzle Alignment

[0419]All of the nozzles within a print head are aligned to sub-micron
accuracy by the 0.5 micron stepper used for the lithography of the print
head. Nozzle alignment of two 4'' print heads to make an A4 page width
print head is achieved with the aid of mechanical alignment features on
the print head chips. This allows automated mechanical alignment (by
simply pushing two print head chips together) to within 1 micron. If
finer alignment is required in specialized applications, 4'' print heads
can be aligned optically.

No Satellite Drops

[0420]The very small drop size (1 pl) and moderate drop velocity (3 m/s)
eliminates satellite drops, which are a major source of image quality
problems. At around 4 m/s, satellite drops form, but catch up with the
main drop. Above around 4.5 m/s, satellite drops form with a variety of
velocities relative to the main drop. Of particular concern is satellite
drops which have a negative velocity relative to the print head, and
therefore are often deposited on the print head surface. These are
difficult to avoid when high drop velocities (around 10 m/s) are used.

Laminar Air Flow

[0421]The low drop velocity requires laminar airflow, with no eddies, to
achieve good drop placement on the print medium. This is achieved by the
design of the print head packaging. For `plain paper` applications and
for printing on other `rough` surfaces, higher drop velocities are
desirable. Drop velocities to 15 m/s can be achieved using variations of
the design dimensions. It is possible to manufacture 3 color photographic
print heads with a 4 m/s drop velocity, and 4 color plain-paper print
heads with a 15 m/s drop velocity, on the same wafer. This is because
both can be made using the same process parameters.

No Misdirected Drops

[0422]Misdirected drops are eliminated by the provision of a thin rim
around the nozzle, which prevents the spread of a drop across the print
head surface in regions where the hydrophobic coating is compromised.

No Thermal Crosstalk

[0423]When adjacent actuators are energized in Bubblejet or other thermal
ink jet systems, the heat from one actuator spreads to others, and
affects their firing characteristics. In IJ46 print heads, heat diffusing
from one actuator to adjacent actuators affects both the heater layer and
the bend-cancelling layer equally, so has no effect on the paddle
position. This virtually eliminates thermal crosstalk.

No Fluidic Crosstalk

[0424]Each simultaneously fired nozzle is at the end of a 300 micron long
ink inlet etched through the (thinned) wafer. These ink inlets are
connected to large ink channels with low fluidic resistance. This
configuration virtually eliminates any effect of drop ejection from one
nozzle on other nozzles.

No Structural Crosstalk

[0425]This is a common problem with piezoelectric print heads. It does not
occur in IJ46 print heads.

Permanent Print Head

[0426]The IJ46 print heads can be permanently installed. This dramatically
lowers the production cost of consumables, as the consumable does not
need to include a print head.

No Kogation

[0427]Kogation (residues of burnt ink, solvent, and impurities) is a
significant problem with Bubblejet and other thermal ink jet print heads.
IJ46 print heads do not have this problem, as the ink is not directly
heated.

No Cavitation

[0428]Erosion caused by the violent collapse of bubbles is another problem
that limits the life of Bubblejet and other thermal ink jet print heads.
IJ46 print heads do not have this problem because no bubbles are formed.

No Electromigration

[0429]No metals are used in IJ46 print head actuators or nozzles, which
are entirely ceramic. Therefore, there is no problem with
electromigration in the actual ink jet devices. The CMOS metalization
layers are designed to support the required currents without
electromigration. This can be readily achieved because the current
considerations arise from heater drive power, not high speed CMOS
switching.

Reliable Power Connections

[0430]While the energy consumption of IJ46 print heads are fifty times
less than thermal ink jet print heads, the high print speed and low
voltage results in a fairly high electrical current consumption. Worst
case current for a photographic IJ46 print head printing in two seconds
from a 3 Volt supply is 4.9 Amps. This is supplied via copper busbars to
256 bond pads along the edge of the chip. Each bond pad carries a maximum
of 40 mA. On chip contacts and vias to the drive transistors carry a peak
current of 1.5 mA for 1.3 microseconds, and a maximum average of 12 mA.

No Corrosion

[0431]The nozzle and actuator are entirely formed of glass and titanium
nitride (TiN), a conductive ceramic commonly used as metalization barrier
layers in CMOS devices. Both materials are highly resistant to corrosion.

No Electrolysis

[0432]The ink is not in contact with any electrical potentials, so there
is no electrolysis.

No Fatigue

[0433]All actuator movement is within elastic limits, and the materials
used are all ceramics, so there is no fatigue.

No Friction

[0434]No moving surfaces are in contact, so there is no friction.

No Stiction

[0435]The IJ46 print head is designed to eliminate stiction, a problem
common to many MEMS devices. Stiction is a word combining "stick" with
"friction" and is especially significant at the in MEMS due to the
relative scaling of forces. In the IJ46 print head, the paddle is
suspended over a hole in the substrate, eliminating the
paddle-to-substrate stiction which would otherwise be encountered.

No Crack Propagation

[0436]The stresses applied to the materials are less than 1% of that which
leads to crack propagation with the typical surface roughness of the TiN
and glass layers. Corners are rounded to minimize stress `hotspots`. The
glass is also always under compressive stress, which is much more
resistant to crack propagation than tensile stress.

No Electrical Poling Required

[0437]Piezoelectric materials must be poled after they are formed into the
print head structure. This poling requires very high electrical field
strengths--around 20,000 V/cm. The high voltage requirement typically
limits the size of piezoelectric print heads to around 5 cm, requiring
100,000 Volts to pole. IJ46 print heads require no poling.

No Rectified Diffusion

[0438]Rectified diffusion--the formation of bubbles due to cyclic pressure
variations--is a problem that primarily afflicts piezoelectric ink jets.
IJ46 print heads are designed to prevent rectified diffusion, as the ink
pressure never falls below zero.

Elimination of the Saw Street

[0439]The saw street between chips on a wafer is typically 200 microns.
This would take 26% of the wafer area. Instead, plasma etching is used,
requiring just 4% of the wafer area. This also eliminates breakage during
sawing.

Lithography Using Standard Steppers

[0440]Although IJ46 print heads are 100 mm long, standard steppers (which
typically have an imaging field around 20 mm square) are used. This is
because the print head is `stitched` using eight identical exposures.
Alignment between stitches is not critical, as there are no electrical
connections between stitch regions. One segment of each of 32 print heads
is imaged with each stepper exposure, giving an `average` of 4 print
heads per exposure.

Integration of Full Color on a Single Chip

[0441]IJ46 print heads integrate all of the colors required onto a single
chip. This cannot be done with page width `edge shooter` ink jet
technologies.

Wide Variety of Inks

[0442]IJ46 print heads do not rely on the ink properties for drop
ejection. Inks can be based on water, microemulsions, oils, various
alcohols, MEK, hot melt waxes, or other solvents. IJ46 print heads can be
`tuned` for inks over a wide range of viscosity and surface tension. This
is a significant factor in allowing a wide range of applications.

Laminar Air Flow with no Eddies

[0443]The print head packaging is designed to ensure that airflow is
laminar, and to eliminate eddies. This is important, as eddies or
turbulence could degrade image quality due to the small drop size.

Drop Repetition Rate

[0444]The nominal drop repetition rate of a photographic IJ46 print head
is 5 kHz, resulting in a print speed of 2 second per photo. The nominal
drop repetition rate for an A4 print head is 10 kHz for 30+ ppm A4
printing. The maximum drop repetition rate is primarily limited by the
nozzle refill rate, which is determined by surface tension when operated
using non-pressurized ink. Drop repetition rates of 50 kHz are possible
using positive ink pressure (around 20 kPa). However, 34 ppm is entirely
adequate for most low cost consumer applications. For very high-speed
applications, such as commercial printing, multiple print heads can be
used in conjunction with fast paper handling. For low power operation
(such as operation from 2 AA batteries) the drop repetition rate can be
reduced to reduce power.

Low Head-to-Paper Speed

[0445]The nominal head to paper speed of a photographic IJ46 print head is
only 0.076 m/sec. For an A4 print head it is only 0.16 m/sec, which is
about a third of the typical scanning ink jet head speed. The low speed
simplifies printer design and improves drop placement accuracy. However,
this head-to-paper speed is enough for 34 ppm printing, due to the page
width print head. Higher speeds can readily be obtained where required.

High Speed CMOS not Required

[0446]The clock speed of the print head shift registers is only 14 MHz for
an A4/letter print head operating at 30 ppm. For a photograph printer,
the clock speed is only 3.84 MHz. This is much lower than the speed
capability of the CMOS process used. This simplifies the CMOS design, and
eliminates power dissipation problems when printing near-white images.

Fully Static CMOS Design

[0447]The shift registers and transfer registers are fully static designs.
A static design requires 35 transistors per nozzle, compared to around 13
for a dynamic design. However, the static design has several advantages,
including higher noise immunity, lower quiescent power consumption, and
greater processing tolerances.

Wide Power Transistor

[0448]The width to length ratio of the power transistor is 688. This
allows a 4 Ohm on-resistance, whereby the drive transistor consumes 6.7%
of the actuator power when operating from 3V. This size transistor fits
beneath the actuator, along with the shift register and other logic. Thus
an adequate drive transistor, along with the associated data distribution
circuits, consumes no chip area that is not already required by the
actuator.

[0449]There are several ways to reduce the percentage of power consumed by
the transistor: increase the drive voltage so that the required current
is less. Reduce the lithography to less than 0.5 micron, use BiCMOS or
other high current drive technology, or increase the chip area, allowing
room for drive transistors which are not underneath the actuator.
However, the 6.7% consumption of the present design is considered a
cost-performance optimum.

[0499]Similar capability print heads are unlikely to become available from
the established ink jet manufacturers in the near future. This is because
the two main contenders--thermal ink jet and piezoelectric ink jet--each
have severe fundamental problems meeting the requirements of the
application.

[0500]The most significant problem with thermal ink jet is power
consumption. This is approximately 100 times that required for these
applications, and stems from the energy-inefficient means of drop
ejection. This involves the rapid boiling of water to produce a vapor
bubble which expels the ink. Water has a very high heat capacity, and
must be superheated in thermal ink jet applications. The high power
consumption limits the nozzle packing density, as

[0501]The most significant problem with piezoelectric ink jet is size and
cost. Piezoelectric crystals have a very small deflection at reasonable
drive voltages, and therefore require a large area for each nozzle. Also,
each piezoelectric actuator must be connected to its drive circuit on a
separate substrate. This is not a significant problem at the current
limit of around 300 nozzles per print head, but is a major impediment to
the fabrication of page width print heads with 19,200 nozzles.

[0503]In the preferred embodiment, a paddle is formed with a "poker"
device attached in a central portion thereof such that, during movement
of the paddle, the poker device pokes any unwanted foreign body or
material which should congregate around the nozzle, out of the nozzle.
The poker can be formed during fabrication of the ink ejection nozzle
arrangement by means of a chemical mechanical planarization step with,
preferably, the formation being a byproduct of the normal formation steps
for forming the ink ejection nozzle on arrangement on a semi-conductor
wafer utilizing standard MEMS processing techniques.

[0504]Additionally, in order to restrict the amount of wicking and the
opportunities for wicking, an actuator slot guard is provided, formed on
the bend actuator itself, closely adjacent to the actuator slot so as to
restrict the opportunities for flow of fluid out of the nozzle chamber
due to surface tension effects.

[0505]Turning now to FIG. 1 to FIG. 3 there will now be explained the
operational principles of the preferred embodiment. In FIG. 1, there is
illustrated a nozzle arrangement 201 which is formed on the substrate 202
which can comprise a semi-conductor substrate or the like. The
arrangement 201 includes a nozzle chamber 203 which is normally filled
with ink so as to form a meniscus 204 which surrounds a nozzle rim 205. A
thermal bend actuator device 206 is attached to post 207 and includes a
conductive heater portion 209 which is normally balanced with a
corresponding layer 210 in thermal equilibrium. The actuator 206 passes
through a slot in the wall 212 of the nozzle chamber and inside forms a
nozzle ejection paddle 213. On the paddle 213 is formed a "poker" 215
which is formed when forming the walls of the nozzle chamber 203. Also
formed on the actuator 206 is a actuator slot protection barrier 216. An
ink supply channel 217 is also formed through the surface of the
substrate 202 utilizing highly anisotropic etching of the substrate 202.
During operation, ink flows out of the nozzle chamber 203 so as to form a
layer 219 between the slot in the wall 212 and the actuator slot
protection barrier 216. The protection barrier is profiled to
substantially mate with the slot but to be slightly spaced apart
therefrom so that any meniscus eg. 219 is of small dimensions.

[0506]Next, as illustrated in FIG. 2, when it is desired to eject a drop
from the nozzle chamber 203, the bottom conductive thermal actuator 209
is heated electrically so as to undergo a rapid expansion which in turn
results in the rapid upward movement of the paddle 213. The rapid upward
movement of the paddle 213 results in ink flow out of the nozzle so as to
form bulging ink meniscus 204. Importantly, the movement of the actuator
206 results in the poker 215 moving up through the plane of the nozzle
rim so as to assist in the ejection of any debris which may be in
vicinity of the nozzle rim 205.

[0507]Further, the movement of the actuator 206 results in a slight
movement of the actuator slot protection barrier 216 which maintains
substantially the small dimensioned meniscus 219 thereby reducing the
opportunity for ink wicking along surfaces. Subsequently, the conductive
heater 209 is turned off and the actuator 206 begins to rapidly return to
its original position. The forward momentum of the ink around meniscus
204 in addition to the backflow due to return movement of the actuator
2026 results in a general necking and breaking of the meniscus 204 so as
to form a drop.

[0508]The situation a short time later is as illustrated in FIG. 3 where a
drop 220 proceeds to the print media and the meniscus collapses around
poker 215 so as to form menisci 222, 223. The formation of the menisci
222, 223 result in a high surface tension pressure being exerted in the
nozzle chamber 203 which results in ink being drawn into the nozzle
chamber 203 via ink supply channel 217 so as to rapidly refill the nozzle
chamber 203. The utilization of the poker 215 increases the speed of
refill in addition to ensuring that no air bubble forms within the nozzle
chamber 203 by means of the meniscus attaching to the surface of the
nozzle paddle 213 and remaining there. The poker 215 ensures that the
meniscus eg. 222, 223 will run along the poker 215 so as to refill in the
nozzle chamber. Additionally, the area around the actuator slot barrier
216 remains substantially stable minimizing the opportunities for wicking
therefrom.

[0509]Turning now to FIG. 4 there is illustrated a side perspective view
of a single nozzle arrangement 201 shown in sections. FIG. 5 illustrates
a side perspective view of a single nozzle including a protective shroud
230. The central poker 215 and aperture card 216 are as previously
discussed. The construction of the arrangement of FIGS. 4 and 5 can be as
a result of the simple modification of deep mask steps utilized in the
construction of the nozzle arrangement in Australian Provisional Patent
Application PP6534 (the contents of which are specifically incorporated
by cross-reference) so as to include the poker 215 and guard 216. The
poker and guard are constructed primarily by means of a chemical
mechanical planarization step which is illustrated schematically in FIG.
6 to FIG. 8. The poker 215 and guard 216 are constructed by depositing a
surface layer 232 on a sacrificial layer 231 which includes a series of
etched vias eg. 233. Subsequently, as illustrated in FIG. 7, the top
layer is chemically and mechanically planarized off so as to leave the
underlying structure 235 which is attached to lower structural layers
236. Subsequently, as illustrated in FIG. 8, the sacrificial layer 231 is
etched away leaving the resulting structure as required.

[0510]It would be appreciated by a person skilled in the art that numerous
variations and/or modifications may be made to the present invention as
shown in the specific embodiments without departing from the spirit or
scope of the invention as broadly described. The present embodiments are,
therefore, to be considered in all respect to be illustrative and not
restrictive.